Fix weakref callback
Fix weakref callback

I thought `0` would be a C int, but it was a
Python int. Ergo, it was called when the weak ref
was broken, and an exception was triggered (and
promptly ignored).
danielballan/PyAV,PyAV-Org/PyAV,mikeboers/PyAV,pupil-labs/PyAV,mikeboers/PyAV,PyAV-Org/PyAV,xxr3376/PyAV,mcpv/PyAV,mcpv/PyAV,pupil-labs/PyAV,mcpv/PyAV,danielballan/PyAV,pupil-labs/PyAV,markreidvfx/PyAV,pupil-labs/PyAV,markreidvfx/PyAV,danielballan/PyAV,markreidvfx/PyAV,xxr3376/PyAV,xxr3376/PyAV