Freeze break request: fix metacity crash and session corruption

["Elijah Newren" <newren gmail com>]

Hi,

As reported by both Ubuntu (Sebastien) and Red Hat (Ray), if the user
decides to save their session on logout then metacity currently will
crash and the session will get saved without metacity, leaving the
user running without a window manager on the subsequent login.  Really
nasty.  The problem was code with the logic:

  - get the displays
  - do stuff with the displays
  - set displays to NULL since we won't use it anymore
  - use displays one more time (oops -- guaranteed crash!)

The patch merely switches the order of steps 3 and 4; it's a very
trivial fix.  I should be publically beaten for forgetting to check
for accepted-commit-now patches before relevant freezes, or this would
have been committed already.

Thanks,
Elijah