canvas/stackedwidget: Check if the new geometry is the same as the old

Do nothing if they are the same. This is to prevent a possible
infinite recursion.

Equivalent-to: biolab/orange-canvas-core@0fa9053

Author: ales-erjavec

Orange/canvas/gui/stackedwidget.py

@@ -57,6 +57,7 @@ class StackLayout(QStackedLayout):
 
     """
     def __init__(self, parent=None):
+        self.__rect = QRect()
         QStackedLayout.__init__(self, parent)
         self.currentChanged.connect(self._onCurrentChanged)
 
@@ -85,7 +86,16 @@ def maximumSize(self):
         else:
             return QStackedLayout.maximumSize(self)
 
+    def geometry(self):
+        # Reimplemented due to QTBUG-47107.
+        return QRect(self.__rect)
+
     def setGeometry(self, rect):
+        # type: (QRect) -> None
+        if rect == self.__rect:
+            return
+        self.__rect = QRect(rect)
+
         QStackedLayout.setGeometry(self, rect)
         for i in range(self.count()):
             w = self.widget(i)