avformat/mxfdec: Check edit unit for overflow in mxf_set_current_edit_unit()

Fixes: signed integer overflow: 9223372036854775807 + 1 cannot be represented in type 'long'
Fixes: 392672068/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-6232335892152320

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Tomas Härdin <git@haerdin.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfdec.c

@@ -3956,7 +3956,7 @@ static int64_t mxf_set_current_edit_unit(MXFContext *mxf, AVStream *st, int64_t
     int64_t new_edit_unit;
     MXFIndexTable *t = mxf_find_index_table(mxf, track->index_sid);
 
-    if (!t || track->wrapping == UnknownWrapped)
+    if (!t || track->wrapping == UnknownWrapped || edit_unit > INT64_MAX - track->edit_units_per_packet)
         return -1;
 
     if (mxf_edit_unit_absolute_offset(mxf, t, edit_unit + track->edit_units_per_packet, track->edit_rate, NULL, &next_ofs, NULL, 0) < 0 &&