Fix null pointer dereference
Fix null pointer dereference

With some filters, you can call this method with a null value to reset
the pin to its default format. So for applications that may call
SetFormat(nullptr) to reset to a default state, return invalid media
type.

See:
https://docs.microsoft.com/en-us/windows/win32/api/strmif/nf-strmif-iamstreamconfig-setformat

jp9000/libdshowcapture,jp9000/libdshowcapture