Fixed checkstyle errors
Reset the visibility binding properly when the in game state is left.

This also fix an uncritical memory leak: The StateIngame reference could
not be garbage collected properly before, because the HUDScreenLayer
was referencing it implictly through the anonymous binding class.
Fix two null pointer crashes caused by configured but missing modules.

Crashes occured after:
- Creating a new game
- Configuring a new game
Merge PR #1280 by @flo - minor memory leak and a visibility tweak
Merge PR #1279 by @flo - fix NPEs
Merge PR #1278 by @msteiger - checkstyle errors
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