Re #9419. Remove no-op statement.

The getWorkspace method will throw if the workspace is going to be null
so this line is pointless.
Re #9419. Consolidate code that uses the workspace pointer.
Re #9419. Check whether workspace is actually the same one.

The code before was OK if the 'new' workspace was actually still the
same one, but led to an exception if it was a different workspace just
having the same name. In the latter case we need to recreate the
InstrumentActor (as the code always did in the past).
Merge remote-tracking branch 'origin/bugfix/9419_instrumentview_exception_on_replace'