QIcon: Avoid fetching twice the same pixmap

Looks like something went through the reviewer's eyes. This commit
amends 6ec9b34cbb5fa6b1214cc6551002f46f732ba72f.

Change-Id: I59a05361b1cbdf4e5177821d958766ffe3218f16
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>