Check IME info nullability before switching

This moves the nullability check of the input method info outside of the
InputMethodSubtypeSwitchingController, to maintain consistency with
other methods.

Flag: EXEMPT refactor
Bug: 347693610
Test: presubmit
Change-Id: I4141d1c909b8d96fd6ee7bf72cd82a0f2e0ef6d0
2 files changed