Fix circular dependency with tab index and active stack

Only when actually clicking the tab should it change the active extruder index; not when the current index is changed for any other reason.
Next up: Don't change the current index for any other reason.

Contributes to issue CURA-5876.

resources/qml/Menus/ConfigurationMenu/CustomConfiguration.qml

@@ -35,7 +35,7 @@ Item
         anchors.top: header.bottom
         anchors.topMargin: UM.Theme.getSize("default_margin").height
 
-        onCurrentIndexChanged: Cura.ExtruderManager.setActiveExtruderIndex(currentIndex)
+        currentIndex: Math.max(Cura.ExtruderManager.activeExtruderIndex, 0)
 
         Repeater
         {
@@ -53,6 +53,10 @@ Item
                         height: parent.height
                     }
                 }
+                onClicked:
+                {
+                    Cura.ExtruderManager.setActiveExtruderIndex(tabBar.currentIndex)
+                }
             }
         }
     }