dockarea.restoreState corrupts dock state if a dock is present in dictionary but not in area

[sbourdeauducq]

If a dictionary passed to restoreState references a dock name that has not been created by the application, pyqtgraph raises:
Exception: Cannot restore dock state; no dock with name "..."

So far so good, but in this case restoreState also leaves the dock state internally broken and the application unusable (if you simply catch the exception).

Much better behavior would be either:

• not touch the dock state at all if the dictionary does not match it.
• ignore those docks that are present in the dictionary and not in the area (or otherwise have inconsistent information in the dictionary).
• mess up the dock layout but at least leave it possible for the user to rearrange it instead of internally corrupting it.