Added support to SwipeBack for return null destination form as a mean…

…s to de-activate swipeBack if conditions to exit Form are not met (#3622)

* Fixed issue of "oversensitive swipe" #3160. PR as suggested by Shai in Reddit

* Added support to let swipeback destination form be null to prevent swipeBack for example if conditions to exit Form are not met.

CodenameOne/src/com/codename1/ui/util/SwipeBackSupport.java

@@ -98,7 +98,9 @@ public void actionPerformed(ActionEvent evt) {
                         if (x - initialDragX > Display.getInstance().convertToPixels(currentForm.getUIManager().getThemeConstant("backGestureThresholdInt", 5), true)) {
                             dragActivated = true;
                             destinationForm = destination.get();
-                            startBackTransition(currentForm, destinationForm);
+                            if(destinationForm!=null) { //allow destination form to be null to disable swipeback, e.g. if conditions to exit Form are not fulfilled
+                                startBackTransition(currentForm, destinationForm);
+                            }
                         }
                     }
                 }