Fix clang -Wconditional-uninitialized warnings.

src/libespeak-ng/compiledata.c

 	char c;
 	int keyword;
 	int n_tune_names = 0;
-	int done_split;
+	int done_split = 0;
 	int done_onset = 0;
 	int done_last = 0;
 	int n_preset_tunes = 0;

src/libespeak-ng/translate.c

 {
 	int ix;
 	int c;
-	int cc;
+	int cc = 0;
 	unsigned int source_index = 0;
 	unsigned int prev_source_index = 0;
 	int source_index_word = 0;

src/libespeak-ng/wavegen.c

 	signed char c;
 	int sample;
 	int amp;
-	int modn_amp, modn_period;
+	int modn_amp = 1, modn_period;
 	static int agc = 256;
 	static int h_switch_sign = 0;
 	static int cycle_count = 0;