Support for short MP3 files

If we match > 1 frame, and the next frame header is all NULL or a TAG then say that we matched a frame, as we likely reached the end of the file.

lieff/minimp3#125

minimp3.h

@@ -1676,6 +1676,21 @@ static void mp3d_synth_granule( float* qmf_state, float* grbuf, int nbands, int
     }
 }
 
+static int hdr_is_tag( const uint8_t *hdr )
+{
+    return hdr[0] == 'T' && hdr[1] == 'A' && hdr[2] == 'G' && hdr[3] == '\0';
+}
+
+static int hdr_is_null( const uint8_t *hdr )
+{
+    return hdr[0] == '\0' || hdr[1] == '\0' || hdr[2] == '\0' || hdr[3] == '\0';
+}
+
+static int hdr_is_null_or_tag( const uint8_t *hdr )
+{
+    return hdr_is_tag( hdr ) > 0 || hdr_is_null( hdr ) > 0;
+}
+
 static int mp3d_match_frame( const uint8_t* hdr, int mp3_bytes, int frame_bytes )
 {
     int i, nmatch;
@@ -1684,6 +1699,8 @@ static int mp3d_match_frame( const uint8_t* hdr, int mp3_bytes, int frame_bytes
         i += hdr_frame_bytes( hdr + i, frame_bytes ) + hdr_padding( hdr + i );
         if ( i + HDR_SIZE > mp3_bytes )
             return nmatch > 0;
+        if ( hdr_is_null_or_tag( hdr + i ) )
+            return nmatch > 0;
         if ( !hdr_compare( hdr, hdr + i ) )
             return 0;
     }