Actually fail when error occurs in parseFormat

When there's an unsupported number of bits per sample or an invalid
number of samples per block, don't only print an error message using
the error handler, but actually stop parsing the file.

This fixes mpruett#35 (also reported at
https://bugzilla.opensuse.org/show_bug.cgi?id=1026983 and
https://blogs.gentoo.org/ago/2017/02/20/audiofile-heap-based-buffer-overflow-in-imadecodeblockwave-ima-cpp/
)

libaudiofile/WAVE.cpp

@@ -326,13 +326,15 @@ status WAVEFile::parseFormat(const Tag &id, uint32_t size)
 			{
 				_af_error(AF_BAD_NOT_IMPLEMENTED,
 					"IMA ADPCM compression supports only 4 bits per sample");
+				return AF_FAIL;
 			}
 
 			int bytesPerBlock = (samplesPerBlock + 14) / 8 * 4 * channelCount;
 			if (bytesPerBlock > blockAlign || (samplesPerBlock % 8) != 1)
 			{
 				_af_error(AF_BAD_CODEC_CONFIG,
 					"Invalid samples per block for IMA ADPCM compression");
+				return AF_FAIL;
 			}
 
 			track->f.sampleWidth = 16;