Fixed finding variables defined in the upper proc failed

If no new variable was defined in the `eval` method, the variable was hidden from the nested `eval` method.

```ruby
a = 1
p eval %(b = 2; eval %(a)) # => 1 (good)
p eval %(eval %(a)) # => undefined method 'a' (NoMethodError)
```

This issue has occurred since mruby 3.0.0.

1 files changed, 4 insertions, 3 deletions

diff --git a/mrbgems/mruby-compiler/core/parse.y b/mrbgems/mruby-compiler/core/parse.y
index 8e68fa21a..96615e3bb 100644
--- a/mrbgems/mruby-compiler/core/parse.y
+++ b/mrbgems/mruby-compiler/core/parse.y
@@ -286,9 +286,10 @@ local_var_p(parser_state *p, mrb_sym sym)
     const mrb_sym *v = ir->lv;
     int i;
 
-    if (!v) break;
-    for (i=0; i+1 < ir->nlocals; i++) {
-      if (v[i] == sym) return TRUE;
+    if (v) {
+      for (i=0; i+1 < ir->nlocals; i++) {
+        if (v[i] == sym) return TRUE;
+      }
     }
     if (MRB_PROC_SCOPE_P(u)) break;
     u = u->upper;