Support for MP3 files < MAX_FRAME_SYNC_MATCHES

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.

Fixes: lieff#102

minimp3.h

@@ -1654,6 +1654,21 @@ static void mp3d_synth_granule(float *qmf_state, float *grbuf, int nbands, int n
     }
 }
 
+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;
@@ -1662,6 +1677,8 @@ 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;
     }