Need to adjust the stack length of the top-level environment; fix #3819

mrbgems/mruby-bin-mirb/tools/mirb/mirb.c

@@ -544,6 +544,13 @@ done:
         if (args.verbose) {
           mrb_codedump_all(mrb, proc);
         }
+        /* adjest stack length of toplevel environment */
+        if (mrb->c->cibase->env) {
+          struct REnv *e = mrb->c->cibase->env;
+          if (MRB_ENV_STACK_LEN(e) < proc->body.irep->nlocals) {
+            MRB_SET_ENV_STACK_LEN(e, proc->body.irep->nlocals);
+          }
+        }
         /* pass a proc for evaluation */
         /* evaluate the bytecode */
         result = mrb_vm_run(mrb,