fixes crash on level start under Windows 7 64

Windows 7 64 crashes with 
    attempt to index field '?'
when it is time to enter a level (just after intro "flyin" animation).
This check prevents the crash and only places the character at a door if Level:enter is given a valid door for the level.
Merge branch 'patch-1' of git://github.com/lafncow/hawkthorne-journey into tester