Fix wrong icon in Linux (BL-779)

In release builds we occasionally tried to set the icon before
the handle was created. Due to a mono bug this didn't work.
This change sets the icon after the handle got created.
We fixed this in Mono several times before, but it looks like there are some constellations where our fixes don't work. I didn't spend time to create a simple test case that would demonstrate the problem, so I didn't create a mono bug report that we could reference.

Changed the comment to your suggestion.