bugfix: allow both SSSML <audio> and soundicon punctuation

All sound file information goes to soundicon_tab. The contents of the files are not
loaded to memory before they are needed for synthesis.

This removes N_SOUNDICON_SLOTS that divided soundicon_tab into two
parts for unknown reasons.

TODO: LoadConfig() is currently undocumented. The logic should be
moved to LoadVoice() and documented.

src/libespeak-ng/soundicon.c

 #include "speech.h"                   // for path_home, GetFileLength, PATHSEP
 #include "synthesize.h"                   // for samplerate
 
-int n_soundicon_tab = N_SOUNDICON_SLOTS;
+int n_soundicon_tab = 0;
 SOUND_ICON soundicon_tab[N_SOUNDICON_TAB];
 
 
 
 int LookupSoundicon(int c)
 {
-	// Find the sound icon number for a punctuation character
+	// Find the sound icon number for a punctuation character and load the audio file if it's not yet loaded
 	int ix;
 
-	for (ix = N_SOUNDICON_SLOTS; ix < n_soundicon_tab; ix++) {
+	for (ix = 0; ix < n_soundicon_tab; ix++) {
 		if (soundicon_tab[ix].name == c) {
-			if (soundicon_tab[ix].length == 0) {
-				if (LoadSoundFile(NULL, ix, NULL) != ENS_OK)
+			if (soundicon_tab[ix].length == 0) { // not yet loaded, load now
+				if (LoadSoundFile(NULL, ix, NULL) != ENS_OK) {
 					return -1; // sound file is not available
+				}
 			}
 			return ix;
 		}
 
 int LoadSoundFile2(const char *fname)
 {
-	// Load a sound file into one of the reserved slots in the sound icon table
-	// (if it'snot already loaded)
+	// Load a sound file into the sound icon table and memory
+	// (if it's not already loaded)
+	// returns -1 on error or the index of loaded file on success
 
 	int ix;
-	static int slot = -1;
-
 	for (ix = 0; ix < n_soundicon_tab; ix++) {
-		if (((soundicon_tab[ix].filename != NULL) && strcmp(fname, soundicon_tab[ix].filename) == 0))
-			return ix; // already loaded
+		if (((soundicon_tab[ix].filename != NULL) && strcmp(fname, soundicon_tab[ix].filename) == 0)) {
+			// the file information is found. If length = 0 it needs to be loaded to memory
+			if (soundicon_tab[ix].length == 0) {
+				if (LoadSoundFile(NULL, ix, NULL) != ENS_OK)
+					return -1; // sound file is not available
+			}
+			return ix; // sound file already loaded to memory
+		}
 	}
 
-	// load the file into the next slot
-	slot++;
-	if (slot >= N_SOUNDICON_SLOTS)
-		slot = 0;
-
-	if (LoadSoundFile(fname, slot, NULL) != ENS_OK)
+	// load the file into the current slot and increase index
+	if (LoadSoundFile(fname, n_soundicon_tab, NULL) != ENS_OK)
 		return -1;
 
-	soundicon_tab[slot].filename = (char *)realloc(soundicon_tab[ix].filename, strlen(fname)+1);
-	strcpy(soundicon_tab[slot].filename, fname);
-	return slot;
+	soundicon_tab[n_soundicon_tab].filename = (char *)realloc(soundicon_tab[n_soundicon_tab].filename, strlen(fname)+1);
+	strcpy(soundicon_tab[n_soundicon_tab].filename, fname);
+	n_soundicon_tab++;
+	return n_soundicon_tab - 1;
 }

src/libespeak-ng/soundicon.h

 int LoadSoundFile2(const char *fname);
 
 typedef struct {
-        int name;
+        int name; // used for detecting punctuation
         int length;
         char *data;
         char *filename;
 } SOUND_ICON;
 
-#define N_SOUNDICON_TAB  80   // total entries in soundicon_tab
-#define N_SOUNDICON_SLOTS 4    // number of slots reserved for dynamic loading of audio files
+#define N_SOUNDICON_TAB  80   // total entries for dynamic loading of audio files
 
 extern int n_soundicon_tab;
 extern SOUND_ICON soundicon_tab[N_SOUNDICON_TAB];

src/libespeak-ng/synthdata.c

 #include "phoneme.h"                  // for PHONEME_TAB, PHONEME_TAB_LIST
 #include "speech.h"                   // for path_home, GetFileLength, PATHSEP
 #include "mbrola.h"                   // for mbrola_name
-#include "soundicon.h"               // for N_SOUNDICON_SLOTS, soundicon_tab
+#include "soundicon.h"               // for soundicon_tab
 #include "synthesize.h"               // for PHONEME_LIST, frameref_t, PHONE...
 #include "translate.h"                // for Translator, LANGUAGE_OPTIONS
 #include "voice.h"                    // for ReadTonePoints, tone_points, voice
 	char c1;
 	char string[200];
 
-	for (ix = 0; ix < N_SOUNDICON_SLOTS; ix++) {
-		soundicon_tab[ix].filename = NULL;
-		soundicon_tab[ix].data = NULL;
-	}
-
 	sprintf(buf, "%s%c%s", path_home, PATHSEP, "config");
 	if ((f = fopen(buf, "r")) == NULL)
 		return;
 		else if (memcmp(buf, "soundicon", 9) == 0) {
 			ix = sscanf(&buf[10], "_%c %s", &c1, string);
 			if (ix == 2) {
+				// add sound file information to soundicon array
+				// the file will be loaded to memory by LoadSoundFile2()
 				soundicon_tab[n_soundicon_tab].name = c1;
 				soundicon_tab[n_soundicon_tab].filename = strdup(string);
 				soundicon_tab[n_soundicon_tab++].length = 0;