Fix legacy recents crash on Go devices

Go does not have PIP enabled and thus does not put the PipUI component
when starting up System UI service componenets. However, as part of
moving things to legacy recents, we are now always listening to PIP menu
events even with the feature disabled and we hit a NPE since we get a
null component. This CL adds a simple null check and backs out if we
don't have the component.

Bug: 132703125
Test: No longer crashes on KB3 Go device
Change-Id: I55e4fc30dc392a8052850a726e756b03fd4c91f6