[510442] Fix NPE in MergeViewerItemProviderConfiguration

* Register the types NODE_TYPE__EMF_EOBJECT, NODE_TYPE__EMF_RESOURCE,
NODE_TYPE__EMF_RESOURCESET and NODE_TYPE__EMF_COMPARISON to the
WaitViewer instead of the TreeContentMergeViewer. This avoids creating a
TreeContentMergeViewer when no Comparison is
created yet..
* Null-check the comparison within the TreeContentMergeViewer and create
a DummyContentProvider if necessary.

Bug: 510442
Signed-off-by: Stefan Dirix <sdirix@eclipsesource.com>
Change-Id: I69e3f5676e2a99b13b29d42c536664eb9d71fbbf
2 files changed