[IL53] Fix a wrong test.

This test was intended only for cases without a selection, and as
a safety net for cases where the app would pretend the cursor
is at N but we can get P chars from the editor where P > N.

When there is a selection, this is wrong. In the practice it works
because these values are not used in this case, but it's still wrong.

The case where P > N is arguable, but actually I see little reason
to trust the getTextBeforeCursor() method more than the
onUpdate selection method. Plus in the practice, I don't think
we are aware of any app with this bug, and it's probably not a
great idea to be too robust about this as it may encourage wrong
values sent to onUpdateSelection.

Change-Id: I42f2065d7aee668074e6b8e40b259da7e88e16e1