Avoid direct return from ecall(); fix
There's incompatibility left for mruby.
When you return from `ensure` clause, mruby simply ignores the return
value.  CRuby returns from the method squashing the exception raised.
```
def f
no_such_method() # NoMethodError
ensure
return 22
end
p f() # CRuby prints `22`
```
@@ -1652,7 +1652,7 @@ RETRY_TRY_BLOCK:
switch (GETARG_B(i)) {
case OP_R_RETURN:
/* Fall through to OP_R_NORMAL otherwise */
- if (proc->env && !MRB_PROC_STRICT_P(proc)) {
+ if (ci->acc >=0 && proc->env && !MRB_PROC_STRICT_P(proc)) {
struct REnv *e = top_env(mrb, proc);
if (!MRB_ENV_STACK_SHARED_P(e)) {
