Blender Git Loki

Windows: Ignore context record for backtrace is address is 0.

T76602 reported a crash with the exception address being 0,
this stack naturally could not be walked and no backtrace was
reported for the main thread. Which would have been helpful.

This change modifies the behaviour of the crash handler to ignore
the context record if it contains no useful information and
walk the current stack to get some information about what lead
to the crash.