Fix bug in update available root list when deleting root item

nw/gui/mainmenu.py

@@ -75,6 +75,9 @@ class GuiMainMenu(QMenuBar):
     ##
 
     def setAvailableRoot(self):
+        """Update the list of available root folders and set the ones
+        that are active.
+        """
         for itemClass in nwItemClass:
             if itemClass == nwItemClass.NO_CLASS:
                 continue

nw/gui/projtree.py

@@ -469,6 +469,7 @@ class GuiProjectTree(QTreeWidget):
             tIndex = self.indexOfTopLevelItem(trItemS)
             if trItemS.childCount() == 0:
                 self.takeTopLevelItem(tIndex)
+                del self.theProject.projTree[tHandle]
                 self.theParent.mainMenu.setAvailableRoot()
                 self._setTreeChanged(True)
             else: