Add null check for input view.

Add a null check here to prevent NPE.

Fixes: 283621786
Test: drag around pattern view.
Change-Id: I3f71a9747f1c6c7c09225b0b72f6ba5652000d1a

packages/SystemUI/src/com/android/keyguard/KeyguardSecurityContainer.java

@@ -474,7 +474,8 @@ public class KeyguardSecurityContainer extends ConstraintLayout {
                     return false;
                 }
                 // Avoid dragging the pattern view
-                if (mSecurityViewFlipper.getSecurityView().disallowInterceptTouch(event)) {
+                if (mSecurityViewFlipper.getSecurityView() != null
+                        && mSecurityViewFlipper.getSecurityView().disallowInterceptTouch(event)) {
                     return false;
                 }
                 int index = event.findPointerIndex(mActivePointerId);