Because ICCCM pretty much mandates that minimized (aka "iconic") clients are
unmapped. In detail: To go back to normal state, the client should map its
window and for this to work, the window needs to be unmapped.
Thanks to Oleg Shparber for reporting some issue he had with a self-written Qt
program and for providing a simple and short test case.
Signed-off-by: Uli Schlachter <psychon@znc.in>