avoid null dereference

fix a null pointer dereference exposed during 64-bit testing; caused a
crash at the end of recording video. I would have expected a similiar failure
in 32-bit mode, but suspect some code generation + inlining difference optimized
away the dereference in 32-bit mode. Have not identified just where that
happens.

Bug: 16890215
Test: record videos in both 32- and 64-bit modes