Fix showSoftInput crashing when no IME is enabled

This CL adds a shortcut for bindCurrentMethod in
InputMethodBindingController to return NO_IME instead of
crashing in the rare case when no IME is enabled in the system.

Bug: 220125769
Test: atest InputMethodServiceTest#testShowSoftInput_whenAllImesDisabled
(cherry picked from commit 10703584)
Merged-In:I7da6ed7f2b80331c469751b7091c340422df40a8
Simplify getImmDelegate in ImeFocusController

This CL undoes part of [1] making removing a local variable.

[1]: Id4c85be1c0eab51f167ba00fc355386f852c424d

Test: make
(cherry picked from commit d9003399)
Merged-In:I6b890e5536c17dd53722e2c3a781c85dd9d6bdf0

Change-Id: Ic82e3c836c2c078778de1022ebf6c5f78883c1c1