Fix visibility rule for SF traces on Winscope

When traces don't have a visible region object assigned winscope crashes
while loading a SF trace.

Test: Open a SF trace without a visible region object on winscope. It
should no longer crash

Merged-In: I7919a0301ccfb6a0811fd15feb718c8ac0b210b1
Change-Id: I7919a0301ccfb6a0811fd15feb718c8ac0b210b1
1 file changed