LoadSoundFile: Fix char signedness

src/libespeak-ng/soundicon.c

 static espeak_ng_STATUS LoadSoundFile(const char *fname, int index, espeak_ng_ERROR_CONTEXT *context)
 {
 	FILE *f;
-	char *p;
+	unsigned char *p;
 	int length;
 	char fname_temp[100];
 	char fname2[sizeof(path_home)+13+40];
 		fclose(f);
 		return create_file_error_context(context, error, fname);
 	}
-	if ((p = (char *)realloc(soundicon_tab[index].data, length)) == NULL) {
+	if ((p = realloc(soundicon_tab[index].data, length)) == NULL) {
 		fclose(f);
 		return ENOMEM;
 	}
 
 	length = p[40] | (p[41] << 8) | (p[42] << 16) | (p[43] << 24);
 	soundicon_tab[index].length = length / 2; // length in samples
-	soundicon_tab[index].data = p;
+	soundicon_tab[index].data = (char *) p;
 	return ENS_OK;
 }