stream_decoder.c: Fix a memory leak

Leak reported by Secunia Research.

src/libFLAC/stream_decoder.c

@@ -1753,6 +1753,9 @@ FLAC__bool read_metadata_vorbiscomment_(FLAC__StreamDecoder *decoder, FLAC__Stre
 					}
 					memset (obj->comments[i].entry, 0, obj->comments[i].length) ;
 					if (!FLAC__bitreader_read_byte_block_aligned_no_crc(decoder->private_->input, obj->comments[i].entry, obj->comments[i].length)) {
+						/* Current i-th entry is bad, so we delete it. */
+						free (obj->comments[i].entry) ;
+						obj->comments[i].entry = NULL ;
 						obj->num_comments = i;
 						goto skip;
 					}