NPE during build
on shutdown there is no registry anymore

Change-Id: Ibb3b5d87fda5c178036da893a885fe06eccdef9e
Signed-off-by: Joerg Kubitz <jkubitz-eclipse@gmx.de>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/182761
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>