ssml: Avoid spurious voice change event

We should initialize current_voice_id so that ssml processing knows what
voice we currently have, and not try to change it unless really needed.

src/libespeak-ng/readclause.c

@@ -609,6 +609,8 @@ int ReadClause(Translator *tr, char *buf, short *charix, int *charix_top, int n_
 					xml_buf[n_xml_buf] = 0;
 					c2 = ' ';
 
+					if (base_voice.identifier)
+						strcpy(current_voice_id, base_voice.identifier);
 					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) {

tests/ssml/external-entity.expected

@@ -1,5 +1,4 @@
 
-
 hˈɪɹ ɑː͡ɹ ðə pˈæswɜːdz
 
 

tests/ssml/spec-example-1.expected

@@ -1,6 +1,5 @@
 
 
-
 juː hæv fˈɔː͡ɹ nˈuː mˈɛsɪd͡ʒᵻz
 
 ðə fˈɜːst ɪz fɹʌm stˈɛfəni wˈɪljəmz ænd ɚɹˈa͡ɪvd æt