[PATCH] user32: Use font default height if GetTextExtentPoint returns empty rectangle

[Nikolay Sivov]

I just sent a test [1] to confirm that GetTextExtenPoint is not 
responsible in setting 'cy' for empty string case. It confirms that it 
has to be dealt with separately, just like this patch does.

[1] https://www.winehq.org/pipermail/wine-patches/2015-November/144589.html