Fix #715: Need better error messages if MBROLA engine or voice files are missing

src/libespeak-ng/mbrowrap.c

 			    strncmp(buf_ptr, "Input Flush Signal", 18) == 0)
 				continue;
 			*lf = 0;
-			fprintf(stderr, "mbrola: %s\n", buf_ptr);
+			if (strstr(buf_ptr, "mbrola: No such file or directory") != NULL)
+				fprintf(stderr,
+						"mbrola executable was not found. Please install MBROLA!\n");
+			else
+				fprintf(stderr, "mbrola: %s\n", buf_ptr);
 			// is this the last line?
 			if (lf == &buf_ptr[result - 1]) {
 				snprintf(mbr_errorbuf, sizeof(mbr_errorbuf),

src/libespeak-ng/synth_mbrola.c

 
 			if (GetFileLength(path) <= 0)
 				sprintf(path, "/usr/share/mbrola/voices/%s", mbrola_voice);
+
+			// Show error message
+			if (GetFileLength(path) <= 0) {
+				fprintf(stderr, "Cannot find MBROLA voice file '%s' in neither of paths:\n"
+						" - /usr/share/mbrola/%s\n"
+						" - /usr/share/mbrola/%s/%s\n"
+						" - /usr/share/mbrola/voices/%s\n"
+						"Please install necessary MBROLA voice!\n",
+						mbrola_voice, mbrola_voice, mbrola_voice, mbrola_voice, mbrola_voice);
+				// Set path back to simple name, otherwise it shows misleading error only for
+				// last unsuccessfully searched path
+				sprintf(path, "%s", mbrola_voice);
+			}
 		}
 	}
 	close_MBR();