avformat/4xm: Consider max_streams on reallocating tracks array

Fixes: OOM
Fixes: 41595/clusterfuzz-testcase-minimized-ffmpeg_dem_FOURXM_fuzzer-6355979363549184

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 0dcd95ef)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>