bug#19482: Changing to big font cause display problem

[张海君]

Open emacs, and run the following code:
(set-frame-font "Menlo:size=30")

Then text in "*scratch*" buffer disappeared and I can't make the text visible 
with scrolling up or down.
After resizing Emacs's window size, text is visible.

It seems that after changing font size Emacs doesn't known the real window size 
and so can't display
correctly.