It's difficult to automatically detect calling an invalid, non-NULL
pointer when getting a stack trace. This manually recreates what we do
for calls to NULL since commit 412ce956b0 ("libdrgn: x86_64: unwind
call when pc is 0"). This was used to debug the issue fixed by "net:
tcp: fix crashes trying to free half-baked MTU probes" [1].
1: https://lore.kernel.org/all/20231010173651.3990234-1-kuba@kernel.org/T/
Signed-off-by: Omar Sandoval <osandov@osandov.com>
