[automerger skipped] Add null check for mCallback in AutoFillUI am: cf4598e1 -s ours

am skip reason: Merged-In I7d3f8fe399cb4e83f5f5fb80e27d232dad3b5b74 with SHA-1 1969fb56 is already in history

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/3472096



Change-Id: I69f52f89b0449afa704ae6619342afb9345f25bb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>