Fix NPE with OverlayTransformApiHelper

OverlayTransformApiHelper is only created if the WindowAndroid has a
Window.

Add an extra check when the object is actually created before being
used.

Change-Id: I835b8101069c8ee3c03bec9e71c63b1e4b66c751
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3865018
Reviewed-by: Bo Liu <boliu@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1042176}

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

@@ -1064,7 +1064,8 @@ void onOverlayTransformUpdated() {
     @CalledByNative
     private @OverlayTransform int getOverlayTransform() {
         int overlayTransform = OverlayTransform.INVALID;
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S_V2) {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S_V2
+                && mOverlayTransformApiHelper != null) {
             overlayTransform = mOverlayTransformApiHelper.getOverlayTransform();
         }
         // Fallback to display rotation