FrameCapture: Add override for Glsizei* types. Fix capturing glGetSynciv with null lengths on Linux. When calling the default WriteParamValueReplay handler with a nullptr, ostream on Linux will write `(nil)`. This fixes retracing all traces containing glGetSynciv calls with null lengths. Add a NullLength test to FenceSyncTests that used to fail in the capture_replay_tests. Test: capture_replay_tests.py --gtest_filter=FenceSyncTest.NullLength/* Bug: angleproject:7071 Bug: angleproject:6808 Change-Id: I0a2bd4db744ce2a026cd932ba0f2f4747672fcc8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3526653 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>