Issue #1602 - Make sure we have a JSObject before trying to get global.

Dynamic script loading/unloading (thank you modules) can yank the script
out from under us before the JS API for it is initialized, leading to
null deref crashes.
This adds a simple check if the passed-in object is sane and present.
Resolves #1602

dom/base/ScriptSettings.cpp

@@ -485,7 +485,13 @@ AutoJSAPI::Init(nsIGlobalObject* aGlobalObject)
 bool
 AutoJSAPI::Init(JSObject* aObject)
 {
-  return Init(xpc::NativeGlobal(aObject));
+  nsIGlobalObject* global = nullptr;
+  if (aObject)
+    global = xpc::NativeGlobal(aObject);
+  if (global)
+    return Init(global);
+  else
+    return false;
 }
 
 bool