Refine missing InputBindResult

The SUCCESS_WITH_ACCESSIBILITY_SESSION result code
was introduced from CL[1].

-. Add the result code into getString() to avoid the
   unknown case.
-. Add comment for the result code.

[1]: Ia651a811093a939d00c081be1961e24ed3ad0356

Bug: 236920321
Test: presubmit
Change-Id: Ieb567237ad0a9cbde6eee47dbbd6c6609eb46688