In certain situations during application startup no MWindow is yet set
as selected to the application. This lead to a NPE when assuming that a
selection always exists to get the context from. In those cases take the
context from the first window when existent.

Signed-off-by: Karsten Thoms <karsten.thoms@karakun.com>
Change-Id: If68e1ea80f2e3d077386ff02a8b09c969f5c62bb