klatt: Fix out-of-bound access (#2074)

src/libespeak-ng/klatt.c

 		if (wdata->mix_wavefile_ix < wdata->n_mix_wavefile) {
 			if (wdata->mix_wave_scale == 0) {
 				// a 16 bit sample
-				c = wdata->mix_wavefile[wdata->mix_wavefile_ix+1];
-				sample = wdata->mix_wavefile[wdata->mix_wavefile_ix] + (c * 256);
+				c = wdata->mix_wavefile[wdata->mix_wavefile_ix+wdata->mix_wavefile_offset+1];
+				sample = wdata->mix_wavefile[wdata->mix_wavefile_ix+wdata->mix_wavefile_offset] + (c * 256);
 				wdata->mix_wavefile_ix += 2;
 			} else {
 				// a 8 bit sample, scaled
-				sample = (signed char)wdata->mix_wavefile[wdata->mix_wavefile_ix++] * wdata->mix_wave_scale;
+				sample = (signed char)wdata->mix_wavefile[wdata->mix_wavefile_offset+wdata->mix_wavefile_ix++] * wdata->mix_wave_scale;
 			}
 			int z2 = sample * wdata->amplitude_v / 1024;
 			z2 = (z2 * wdata->mix_wave_amp)/40;
 			temp += z2;
+
+			if ((wdata->mix_wavefile_ix + wdata->mix_wavefile_offset) >= wdata->mix_wavefile_max)  // reached the end of available WAV data
+				wdata->mix_wavefile_offset -= (wdata->mix_wavefile_max*3)/4;
 		}
 
 		if (kt_globals.fadein < 64) {

tests/klatt.test

 # and run needed checks before
 is_hash
 # call actual test functions
-test_wav en+klatt  "8155a2249db8f6fe5f3b1d4fd00c35d09ceb6c82" "The quick brown fox jumps over the lazy dog"
-test_wav en+klatt2 "90559a2ff9973c3ccf1eb7e71579fedfedbd3c67" "The quick brown fox jumps over the lazy dog"
-test_wav en+klatt3 "a636bc97d68fbec753c7cecc718b539c87627095" "The quick brown fox jumps over the lazy dog"
-test_wav en+klatt4 "653e243019c9462c7a9a90f4b03326d45b45f41c" "The quick brown fox jumps over the lazy dog"
-test_wav en+klatt5 "6665329b413244b9846533ce207f0ee3d6e55094" "The quick brown fox jumps over the lazy dog"
+test_wav en+klatt  "696213dbbceecf20c3f80d771aab5757e05181c0" "The quick brown fox jumps over the lazy dog"
+test_wav en+klatt2 "e55bf0a5cd96d648177f743557c67a791da03f7b" "The quick brown fox jumps over the lazy dog"
+test_wav en+klatt3 "9ed890d032b1bed4a4ef1e3380b68133d0342429" "The quick brown fox jumps over the lazy dog"
+test_wav en+klatt4 "77243123d96113ab747200c5312e4945af4e16f3" "The quick brown fox jumps over the lazy dog"
+test_wav en+klatt5 "6426725d6c5a9053862a5251ff9c1e0a58c29e9b" "The quick brown fox jumps over the lazy dog"