Bug 1354810, CycleCollectedJSContext::Get() needs to be null-checked, r=baku

dom/promise/Promise.cpp

@@ -570,6 +570,9 @@ Promise::PerformWorkerMicroTaskCheckpoint()
   MOZ_ASSERT(!NS_IsMainThread(), "Wrong thread!");
 
   CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  if (!context) {
+    return;
+  }
 
   for (;;) {
     // For a normal microtask checkpoint, we try to use the debugger microtask
@@ -604,6 +607,9 @@ Promise::PerformWorkerDebuggerMicroTaskCheckpoint()
   MOZ_ASSERT(!NS_IsMainThread(), "Wrong thread!");
 
   CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  if (!context) {
+    return;
+  }
 
   for (;;) {
     // For a debugger microtask checkpoint, we always use the debugger microtask