[tracker] tracker-extract: Clarify a magic number

[Philip Withnall <pwithnall src gnome org>]

commit 35c739862e5ba232b8e364653e8dc92683f242e6
Author: Philip Withnall <withnall endlessm com>
Date:   Sun Feb 5 16:06:44 2017 +0100

    tracker-extract: Clarify a magic number
    
    Looks like this is the value of the header and frame sizes.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=778206

 src/tracker-extract/tracker-extract-mp3.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-mp3.c b/src/tracker-extract/tracker-extract-mp3.c
index 32e4ad9..6be6e71 100644
--- a/src/tracker-extract/tracker-extract-mp3.c
+++ b/src/tracker-extract/tracker-extract-mp3.c
@@ -2206,7 +2206,7 @@ parse_id3v20 (const gchar          *data,
        guint tsize;
        guint pos;
 
-       if ((size < 16) ||
+       if ((size < header_size + frame_size) ||
            (data[0] != 0x49) ||
            (data[1] != 0x44) ||
            (data[2] != 0x33) ||