Harden asInstanceOfOpt to be robust for nulls or reflection crashes.
Don't create a reconciler for non-editor source configurations.

In the Syntax Coloring preview pane we create a source viewer without an
editor. The reconciler needs an editor to get to the compilation unit, so
we don't attach a reconciler in this case (there won't be any editing).

We might need to revisit this if we ever want to use a source viewer outside
an editor (with reconciliation capabilities).
Merge pull request #596 from dragos/issue/fix-quiescence-syntax-coloring-window-crash

Fix syntax coloring window crash