segfault on closing

[fdarvas]

Occasionally the detector produces a segfault in line 398 in bindings.py - specifically self.libc.apriltag_detector_destroy(self.tag_detector_ptr) causes the segfault
I am using python 3.8 on Ubuntu 20.04 in a WSL box - but this happens on native ubuntu installations as well.

I am running this with 48 threads in the detector.

After running it through the debugger, this turns out to be the same issue as #34:

Thread 1 "python3" received signal SIGSEGV, Segmentation fault.
0x00007fff94fe8306 in quick_decode_uninit () from /usr/local/lib/python3.8/dist-packages/pupil_apriltags/lib/libapriltag.so.3.1.0