EventLoopProgressMonitor purpose was to support running blocking tasks
*on* UI thread, not the other way around. However, if UI task passes
EventLoopProgressMonitor to the code that runs on non UI thread, bad
things will happen.

We should go into Display code only if EventLoopProgressMonitor is used
on UI thread.

Change-Id: I44f37786065f5958f6e54f5fbce33bd2b9cc83a4
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>