Bug 1781250 - Don't crash in RecvIsWindowSupportingProtectedMedia when fuzzing. r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D152756

dom/ipc/BrowserParent.cpp

@@ -4010,6 +4010,9 @@ mozilla::ipc::IPCResult BrowserParent::RecvIsWindowSupportingProtectedMedia(
       FxRWindowManager::GetInstance()->IsFxRWindow(aOuterWindowID);
   aResolve(!isFxrWindow);
 #else
+#  ifdef FUZZING_SNAPSHOT
+  return IPC_FAIL(this, "Should only be called on Windows");
+#  endif
   MOZ_CRASH("Should only be called on Windows");
 #endif