restore proc after restoring from fiber; ref #1766

src/vm.c

@@ -954,6 +954,7 @@ mrb_context_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int
         ci = mrb->c->ci;
         if (!ci->target_class) { /* return from context modifying method (resume/yield) */
           if (!MRB_PROC_CFUNC_P(ci[-1].proc)) {
+            proc = ci[-1].proc;
             irep = ci[-1].proc->body.irep;
             pool = irep->pool;
             syms = irep->syms;