Debugger: Guard QObject property extraction against failures

Nowadays, the [property] section contains only "top level" properties,
inherited ones are available through by expanding the base class.

Task-number: QTCREATORBUG-15798
Change-Id: I40475500a2d20f27145a47fa7ed1e61d4a592c10
Reviewed-by: Robert Loehning <robert.loehning@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

share/qtcreator/debugger/dumper.py

@@ -1460,9 +1460,13 @@ class DumperBase:
                                 self.put('keyencoded="latin1",')
                                 self.putItem(v)
                                 propertyCount += 1
-
-            self.putValue(str('<%s items>' % propertyCount if propertyCount else '<>0 items>'))
-            self.putNumChild(1)
+                self.putItemCount(propertyCount)
+            else:
+                # We need a handle to [x] for the user to expand the item
+                # before we know whether there are actual children. Counting
+                # them is too expensive.
+                self.putNumChild(1)
+                self.putSpecialValue("minimumitemcount", 0)
 
         with SubItem(self, "[methods]"):
             methodCount = self.staticQObjectMethodCount(smo)