text input: always let cursor rect have a width == 1

Instead of using a cursor width of null when a cursor
delegate is set, we should to use a value of 1.
Otherwise the rect we e.g return from cursorRect() will
be invalid. An alternative would be to use the width of
the delegate, but that was found to be controversial.

On iOS we saw a bug with this when telling iOS to position
text spelling popups underneath the cursor. Since the
cursor rect we got was invalid (zero-width), no popup
would show.

Change-Id: Ice51b9a1bd33f331183e3acec61b7d9c0f5163cd
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>