Fix a few more Coverity defects

- NULL-check scrollbars before using it in
WidgetScrollBar::WidgetScrollBar()
- Pass enemy group by reference to MapRenderer::pushEnemyGroup()
- Add missing variable to init list of Animation copy constructor
Merge pull request #1120 from dorkster/fixes

Fix a few more Coverity defects
Merge remote-tracking branch 'upstream/master'