Fix right area being draggable when only rear VC is set

Disallow dragging border from the right if only rear controller is set, and vise versa when right is set but not rear.

SWRevealViewController/SWRevealViewController.m

@@ -1079,10 +1079,14 @@ - (BOOL)_panGestureShouldBegin
     UIView *recognizerView = _panGestureRecognizer.view;
     CGFloat xLocation = [_panGestureRecognizer locationInView:recognizerView].x;
     CGFloat width = recognizerView.bounds.size.width;
-
-    BOOL draggableBorderAllowing = (
-        _frontViewPosition != FrontViewPositionLeft || _draggableBorderWidth == 0.0f ||
-        xLocation <= _draggableBorderWidth || xLocation >= (width - _draggableBorderWidth) );
+
+    BOOL draggableBorderAllowing = (  _frontViewPosition != FrontViewPositionLeft  || _draggableBorderWidth == 0.0f );
+    if (_rearViewController) {
+        draggableBorderAllowing = draggableBorderAllowing || xLocation <= _draggableBorderWidth;
+    }
+    if (_rightViewController) {
+        draggableBorderAllowing = draggableBorderAllowing || xLocation >= (width - _draggableBorderWidth);
+    }
 
     // allow gesture only within the bounds defined by the draggableBorderWidth property
     return draggableBorderAllowing ;