Only capture screenshots if the first paint is ready (MozillaReality#2304)

Author: MortimerGoro

app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java

@@ -978,7 +978,7 @@ public void setFirstDrawCallback(Runnable aRunnable) {
 
     @Override
     public boolean isFirstPaintReady() {
-        return mWidgetPlacement.composited;
+        return mWidgetPlacement != null && mWidgetPlacement.composited;
     }
 
     @Override
@@ -1536,7 +1536,9 @@ public void onPageStart(@NonNull GeckoSession geckoSession, @NonNull String s) {
     public void onPageStop(@NonNull GeckoSession aSession, boolean b) {
         if (mCaptureOnPageStop || !mSession.hasCapturedBitmap()) {
             mCaptureOnPageStop = false;
-            captureImage();
+            if (isFirstPaintReady()) {
+                captureImage();
+            }
         }
     }
 

app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/Windows.java

@@ -973,7 +973,9 @@ public void onTabsClicked() {
 
         // Capture active session snapshots when showing the tabs menu
         for (WindowWidget window: getCurrentWindows()) {
-            window.captureImage();
+            if (window.isFirstPaintReady()) {
+                window.captureImage();
+            }
         }
     }