Change return type of mrb_range_beg_len() from `int` to `mrb_int`.

ref #3411

include/mruby/range.h

@@ -41,7 +41,7 @@ MRB_API struct RRange* mrb_range_ptr(mrb_state *mrb, mrb_value v);
  */
 MRB_API mrb_value mrb_range_new(mrb_state *mrb, mrb_value start, mrb_value end, mrb_bool exclude);
 
-MRB_API int mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc);
+MRB_API mrb_int mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc);
 mrb_value mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, const mrb_value *argv, mrb_value (*func)(mrb_state*, mrb_value, mrb_int));
 
 MRB_END_DECL

src/range.c

@@ -248,7 +248,7 @@ mrb_range_include(mrb_state *mrb, mrb_value range)
   return mrb_bool_value(include_p);
 }
 
-MRB_API int
+MRB_API mrb_int
 mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc)
 {
   mrb_int beg, end;