fixes resize when using maximize

[wjwwood]

Before this, if you maximized the window, you would sometimes get a weird bug where the ogre render area was a different size than the Qt window, e.g.:

(the sphere should be in the center)

[greimela]

I still have a bug after this fix (Ubuntu 16.04 + GNOME 3).

When maximising the window the render window adjusts fine.
But after unmaximising the render window does not adjust to fit the smaller window.

(again, the sphere should be in the center)

[wjwwood]

@greimela I have the exact same setup, but I wasn't able to get that behavior. Can you confirm that you're using the fix (you recompiled and everything)? I just tried it again and couldn't get it to fail with the patch, though it could just be a fluke.

[anhosi]

Works on my machine (Ubuntu 16.10 + Fvwm 2.6.5)

[Martin-Idel]

Also works on my machine (Ubuntu 16.04 + Unity)

[greimela]

Looks like it has something to do with my Ubuntu + Gnome setup.
Let's exclude the problem from this PR for now and I will investigate futher.

[wjwwood]

Ok, I'll merge this then. @greimela can you open a new issue so we don't lose track of this?

[greimela-si]

Done, see #25.