SurfaceComposerClient: Fix potential null de-reference in setRelativeLayer

Obviously the code immediately following the diff was going to segfault if we didnt
return. Looks like just a trivial refactoring error.

Bug: 76148527
Test: Trivial.
Change-Id: I0b575e0d8123d57d8110c9450c7a623c65bcd87c
1 file changed