Bug 1769155 - Null-check win in setter for IsActiveBrowserWindowInternal. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D148914

docshell/base/BrowsingContext.cpp

@@ -2998,6 +2998,7 @@ void BrowsingContext::DidSet(FieldIndex<IDX_IsActiveBrowserWindowInternal>,
       doc->UpdateDocumentStates(DocumentState::WINDOW_INACTIVE, true);
 
       RefPtr<nsPIDOMWindowInner> win = doc->GetInnerWindow();
+      if (win) {
         RefPtr<MediaDevices> devices;
         if (isActivateEvent && (devices = win->GetExtantMediaDevices())) {
           devices->BrowserWindowBecameActive();
@@ -3013,6 +3014,7 @@ void BrowsingContext::DidSet(FieldIndex<IDX_IsActiveBrowserWindowInternal>,
               CanBubble::eYes, Cancelable::eYes, nullptr);
         }
       }
+    }
   });
 }