VirtualJoystick: Fix stick position while screen size changes

Resolve of mavlink#10666, while the QGC window is resizing, both virtual
joysticks are not centered causing dangerous behavior. Now, if the screen
size is changed, both joysticks will be centered while the screen resize
is stopped.

src/QmlControls/JoystickThumbPad.qml

@@ -28,11 +28,18 @@ Item {
 
     QGCMapPalette { id: mapPal }
 
-    onWidthChanged:                     calculateXAxis()
     onStickPositionXChanged:            calculateXAxis()
-    onHeightChanged:                    calculateYAxis()
     onStickPositionYChanged:            calculateYAxis()
     onYAxisPositiveRangeOnlyChanged:    calculateYAxis()
+    onHeightChanged:                    { 
+                                            calculateYAxis()
+                                            reCenter() 
+                                        }
+    onWidthChanged:                     { 
+                                            calculateXAxis()
+                                            reCenter() 
+                                        }
+    //We prevent Joystick to move while the screen is resizing 
 
     function calculateXAxis() {
         if(!_joyRoot.visible) {