Guard against null events passed to onScroll

It appears that on some devices, e1 can be null, which would result in a
crash. This is probably due to manufacturers messing with input handling
of AOSP.

app/src/main/java/com/gaurav/avnc/ui/vnc/TouchHandler.kt

@@ -220,8 +220,9 @@ class TouchHandler(private val viewModel: VncViewModel, private val dispatcher:
         return true
     }
 
-    override fun onScroll(e1: MotionEvent, e2: MotionEvent, dX: Float, dY: Float): Boolean {
-        val startPoint = e1.point()
+    override fun onScroll(e1: MotionEvent?, e2: MotionEvent, dX: Float, dY: Float): Boolean {
+        // As weird as it may be, e1 can be null on some devices
+        val startPoint = e1?.point() ?: return false
         val currentPoint = e2.point()
         val normalizedDx = -dX * swipeSensitivity
         val normalizedDy = -dY * swipeSensitivity