Support "pure" DockWidget in PanelDescription.fromPanel

Fixes taurus-org#1129

MR !940 broke the PanelDescription.fromPanel() when using panels
for which the new attributes were not described.

Make the "fromPanel" robust against this situation.

lib/taurus/qt/qtgui/taurusgui/utils.py

@@ -426,11 +426,11 @@ def fromPanel(panel):
             sharedDataWrite=sharedDataWrite,
             sharedDataRead=sharedDataRead,
             model=model,
-            icon=panel.icon,
-            model_in_config=panel.model_in_config,
-            modifiable_by_user=panel.modifiable_by_user,
-            widget_formatter=panel.widget_formatter,
-            widget_properties=panel.widget_properties
+            icon=getattr(panel, "icon", None),
+            model_in_config=getattr(panel, "model_in_config", None),
+            modifiable_by_user=getattr(panel, "modifiable_by_user", None),
+            widget_formatter=getattr(panel, "widget_formatter", None),
+            widget_properties=getattr(panel, "widget_properties", {})
             )