Propagate exceptions in RemoteInputConnectionImpl

Previously there were cases where we failed to invoke callback used to
implement sync APIs in InputConnection if app's InputConnection failed
due to exceptions, while the IME was still waiting for the callback.

Although such an exception usually triggers an app crash, which
eventually triggers IInputMethodWrapper#unbindInput() to unblock IME's
waiting operation [1], there is no reason to not propagate the failure
through the callback object itself to minimize the blocking time.
This CL just makes it happen.

Note that there is no observable behavior change in the IME client
app.  What this CL does is just completing the callback request before
letting an exception go, which will never change the fate of the IME
client process.

 [1]: Ic65a95eb5d0fd56f505a02fd9083bcf6694b6734
      f87f7508

Fix: 195699814
Test: atest CtsInputMethodTestCases:InputConnectionHandlerTest
Change-Id: I5b88333cfad3cbafe311c6262fa00eff893cd8f1