bcachefs: Fix a null ptr deref

We start doing allocations before the GC thread is created, which means
we need to check for that to avoid a null ptr deref.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
This commit is contained in:
Kent Overstreet 2022-04-10 14:36:10 -04:00 • committed by Kent Overstreet
commit 6e811bbbc2