Fix IMC NPE for try to access view without attach window

Somtimes apk can frequently switch into Immersive Mode, this tip
show will kind of messed while apk immediatelly finish and start again,
if something stucked, immersive mode win will focus enter delayed,
apply instes but still not attached window.

Bug: 351098088
Flag: EXEMPT bugfix
Test: run monkey auto test
Change-Id: I60168c8166f95efcb6f8a56489ddee67e4a084b1