Fixes Touch.AddFingers allowing creating of invalid Finger

Since the fast enter playmode PR,  SubSystemRegistration ordering issue is causing errors on mobile device when using ISX with AppUI.

The issue was causing a benign exception in development build.

Author: MorganHoarau

Packages/com.unity.inputsystem/InputSystem/Runtime/Plugins/EnhancedTouch/Touch.cs

@@ -772,6 +772,14 @@ internal struct FingerAndTouchState
 
             public void AddFingers(Touchscreen screen)
             {
+                // The global touch state may have been reset after EnhancedTouchSupport.Enable() subscribed to device changes.
+                // A device added through that stale subscription would build a Finger with a None mask, which InputStateHistory.updateMask rejects.
+                // Skip until the state is set up again.
+                if (updateMask == InputUpdateType.None)
+                {
+                    return;
+                }
+
                 var touchCount = screen.touches.Count;
                 ArrayHelpers.EnsureCapacity(ref fingers, totalFingerCount, touchCount);
                 for (var i = 0; i < touchCount; ++i)