Workaround for fix a11y crash bug

a11y event will trigger getSpanSize and we will check view type
there and we use cursor to check view type, however, cursor is
null at this timing then cause NPE.
Add null check to prevent NPE and test it will not cause other
a11y side effect.

Fix: 128490497
Test: manual
Test: atest DocumentsUITests
Change-Id: Ic6ddd8db5bf67f559c8855c5adc5e55da99304e7