- fix crash when logging an invalid context
- output to trace even when platform logging is on

Bug: angleproject:3815
Change-Id: I725f5728e1d839e3d8458579ad1958cb775d9ecf
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1769505Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>