Fix potential NULL dereference in Visualizer effect

Bug: 30229821

Test: fixing CL. Existing unit tests still pass.

Change-Id: I6e4abd759d5d2abc3b391e92e2e18f060cab7af0
(cherry picked from commit 874f9e0b8eb0cbe508d15c8c03796c863851f21f)
1 file changed