Address null colorSpace in PDF Device

The previous change adding SkColorSpace support to saveLayer could
result in a nullptr dereference on the PDF backend. This CL adds a
check to avoid that.

See: https://skia-review.googlesource.com/c/skia/+/817338

Bug: b/327017909
Change-Id: I369fd586a49615c2794d8f43cf1974f6ba253b29
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/841677
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
1 file changed