Changes

GlassPaneRenderer: add null check

Change-Id: I4e6a4bee0df529c691c45e4d443f139afea52188
Reviewed-on: https://git.eclipse.org/r/c/scout/org.eclipse.scout.rt/+/183119
Tested-by: Scout Bot <scout-bot@eclipse.org>
Reviewed-by: Beat Schwarzentrub <bsh@bsiag.com>

Table/Tree: improve error message

jQuery objects don't have a good toString(), so the error message would
only contain "[object Object]", which is not very helpful. Use graphics.
debugOutput() instead.

Change-Id: I451d6a900d8b29c321ca81d779ceff88d21ffced
Reviewed-on: https://git.eclipse.org/r/c/scout/org.eclipse.scout.rt/+/183120
Tested-by: Scout Bot <scout-bot@eclipse.org>
Reviewed-by: Beat Schwarzentrub <bsh@bsiag.com>