vi: Fix overflow due to lengthmod (#2103)

phsource/ph_vietnam

   ELSE 
   Vowelout f1=3 f2=2300 300 400  f3=-200 80  len=40 rms=20 brk
   ENDIF
-  lengthmod 12            // longer than 'n'
+  lengthmod 9             // longer than 'n'
   IF thisPh(isWordEnd) THEN 
 	length 163
   ENDIF

src/libespeak-ng/compiledata.c

 #include <sys/stat.h>
 #include <time.h>
 #include <unistd.h>
+#include <assert.h>
 
 #include <espeak-ng/espeak_ng.h>
 #include <espeak-ng/speak_lib.h>
 				break;
 			case i_LENGTH_MOD:
 				value = NextItem(ctx, tNUMBER);
+				assert(value < LENGTH_MOD_LIMIT);
 				ctx->phoneme_out->length_mod = value;
 				break;
 			case i_IPA_NAME:

src/libespeak-ng/setlengths.c

 // indexes are the "length_mod" value for the following phonemes
 
 // use this table if vowel is not the last in the word
-static const unsigned char length_mods_en[100] = {
+static const unsigned char length_mods_en[LENGTH_MOD_LIMIT * LENGTH_MOD_LIMIT] = {
 //	a    ,    t    s    n    d    z    r    N    <- next
 	100, 120, 100, 105, 100, 110, 110, 100,  95, 100, // a  <- next2
 	105, 120, 105, 110, 125, 130, 135, 115, 125, 100, // ,
 };
 
 // as above, but for the last syllable in a word
-static const unsigned char length_mods_en0[100] = {
+static const unsigned char length_mods_en0[LENGTH_MOD_LIMIT * LENGTH_MOD_LIMIT] = {
 //	a    ,    t    s    n    d    z    r    N    <- next
 	100, 150, 100, 105, 110, 115, 110, 110, 110, 100, // a  <- next2
 	105, 150, 105, 110, 125, 135, 140, 115, 135, 100, // ,
 };
 
 
-static const unsigned char length_mods_equal[100] = {
+static const unsigned char length_mods_equal[LENGTH_MOD_LIMIT * LENGTH_MOD_LIMIT] = {
 //	a    ,    t    s    n    d    z    r    N    <- next
 	110, 120, 100, 110, 110, 110, 110, 110, 110, 110, // a  <- next2
 	110, 120, 100, 110, 110, 110, 110, 110, 110, 110, // ,
 	int value2;
 
 	tr->langopts.length_mods0 = tr->langopts.length_mods = length_mod_tabs[value % 100];
-	if ((value2 = value / 100) != 0)
+	if ((value2 = value / (LENGTH_MOD_LIMIT * LENGTH_MOD_LIMIT)) != 0)
 		tr->langopts.length_mods0 = length_mod_tabs[value2];
 }

src/libespeak-ng/synthesize.h

 
 #define i_StressLevel  0x800
 
+#define LENGTH_MOD_LIMIT 10
+
 typedef struct {
 	int pause_factor;
 	int clause_pause_factor;