Clear handle when tree details panel is cleared

.gitignore

@@ -28,6 +28,7 @@ __pycache__
 /nw/assets/sample.zip
 /sample/cache
 /sample/meta
+/sample/versions
 *.bak
 *.lock
 ToC.txt

nw/gui/itemdetails.py

@@ -196,6 +196,8 @@ class GuiItemDetails(QWidget):
     def clearDetails(self):
         """Clear all the data values.
         """
+        self.theHandle = None
+
         self.labelFlag.setPixmap(QPixmap(1, 1))
         self.statusFlag.setPixmap(QPixmap(1, 1))
         self.classFlag.setText("")