Resolve "[abrt] gjs: JS_GetContextPrivate(): gjs-console killed by SIGSEGV"
In certain cases, it's possible that a GObject's dispose handler will try to call into JS code during the shutdown GC. That ought to be stopped with the check for _gjs_context_is_sweeping() in gjs_callback_closure(), but not when the closure is already invalidated; in that case we can't get to the GjsContext pointer, as it will have been nulled out in the GjsClosure struct.
In that case, check first if we have an invalid closure (which is the same as checking that the GjsContext pointer is not null.)
Closes #148 (closed).
Closes #148 (closed)