code cleanup: Move self_closing checks to ProcessSsmlTag()

This is a bit slower since we don't pass n_xml_buf as an argument but
rather get it with a call to wcslen. It is much cleaner though, since
the name ProcessSsmlTag() implies that all processing should be done
there.

src/libespeak-ng/readclause.c

 	int terminator;
 	int found;
 	bool any_alnum = false;
-	bool self_closing;
 	int punct_data = 0;
 	bool is_end_clause;
 	int announced_punctuation = 0;
 					xml_buf[n_xml_buf] = 0;
 					c2 = ' ';
 
-					self_closing = false;
-					if (xml_buf[n_xml_buf-1] == '/') {
-						// a self-closing tag
-						xml_buf[n_xml_buf-1] = ' ';
-						self_closing = true;
-					}
-
-					terminator = ProcessSsmlTag(xml_buf, buf, &ix, n_buf, self_closing, xmlbase, &audio_text, current_voice_id, &base_voice, base_voice_variant_name, &ignore_text, &clear_skipping_text, &sayas_mode, &sayas_start, ssml_stack, &n_ssml_stack, &n_param_stack, (int *)speech_parameters);
+					terminator = ProcessSsmlTag(xml_buf, buf, &ix, n_buf, xmlbase, &audio_text, current_voice_id, &base_voice, base_voice_variant_name, &ignore_text, &clear_skipping_text, &sayas_mode, &sayas_start, ssml_stack, &n_ssml_stack, &n_param_stack, (int *)speech_parameters);
 
 					if (terminator != 0) {
 						buf[ix] = ' ';

src/libespeak-ng/ssml.c

 	}
 }
 
-int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, bool self_closing, const char *xmlbase, bool *audio_text, char *current_voice_id, espeak_VOICE *base_voice, char *base_voice_variant_name, bool *ignore_text, bool *clear_skipping_text, int *sayas_mode, int *sayas_start, SSML_STACK *ssml_stack, int *n_ssml_stack, int *n_param_stack, int *speech_parameters)
+int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, const char *xmlbase, bool *audio_text, char *current_voice_id, espeak_VOICE *base_voice, char *base_voice_variant_name, bool *ignore_text, bool *clear_skipping_text, int *sayas_mode, int *sayas_start, SSML_STACK *ssml_stack, int *n_ssml_stack, int *n_param_stack, int *speech_parameters)
 {
 	// xml_buf is the tag and attributes with a zero terminator in place of the original '>'
 	// returns a clause terminator value.
 	// these tags have no effect if they are self-closing, eg. <voice />
 	static char ignore_if_self_closing[] = { 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0 };
 
+	bool self_closing = false;
+	int len;
+	len = wcslen(xml_buf);
+	if (xml_buf[len - 1] == '/') {
+		// a self-closing tag
+		xml_buf[len - 1] = ' ';
+		self_closing = true;
+	}
+
 	static const MNEM_TAB mnem_phoneme_alphabet[] = {
 		{ "espeak", 1 },
 		{ NULL,    -1 }

src/libespeak-ng/ssml.h

                    char *outbuf,
                    int *outix,
                    int n_outbuf,
-                   bool self_closing,
                    const char *xmlbase,
                    bool *audio_text,
                    char *current_voice_id,