gui: fix uses of uninitialized values

Clang's static analyzer complained about `ui::toRotation(rotationInt)`:
frameworks/native/libs/gui/LayerState.cpp:544:16: warning: 1st function
call argument is an uninitialized value
[clang-analyzer-core.CallAndMessage]

Looks like there're a few other places in the area where we're
doing things with uninit bit patterns. Initializing things to 0 should
at least make us consistent in the face of Parcel read failures.

Bug: None
Test: TreeHugger
Change-Id: I7ef2a71171b9939cb14611deea1f5b7132c54eaf