state.c: check irep reference count overflow.

src/state.c

@@ -4,6 +4,7 @@
 ** See Copyright Notice in mruby.h
 */
 
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <mruby.h>
@@ -110,6 +111,12 @@ void
 mrb_irep_incref(mrb_state *mrb, mrb_irep *irep)
 {
   if (irep->flags & MRB_IREP_NO_FREE) return;
+  if (irep->refcnt == UINT16_MAX) {
+    mrb_garbage_collect(mrb);
+    if (irep->refcnt == UINT16_MAX) {
+      mrb_raise(mrb, E_RUNTIME_ERROR, "too many irep references");
+    }
+  }
   irep->refcnt++;
 }