window: Be more careful when setting initial workspace state

A window may either be sticky because it has been requested as such,
or because it is placed on a non-primary monitor (and the corresponding
preference is set). While we do take the latter into account, we
currently override the sticky state later during initialization;
be a bit more careful there to get the initial state right.

https://bugzilla.gnome.org/show_bug.cgi?id=737178
window: Always set workspace state while constructing

set_workspace_state () returns early when the desired sticky state
and workspace match the current property values, assuming that the
corresponding MRU lists are already correct in that case.
However that might not be the case when we are setting the initial
state, so don't take the shortcut in that case.

https://bugzilla.gnome.org/show_bug.cgi?id=737178