stringio.c: move GC guard

* ext/stringio/stringio.c (strio_write): move GC guard after the
  last using position.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45676 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/stringio/stringio.c

@@ -1170,7 +1170,6 @@ strio_write(VALUE self, VALUE str)
     long len, olen;
     rb_encoding *enc, *enc2;
 
-    RB_GC_GUARD(str);
     if (!RB_TYPE_P(str, T_STRING))
 	str = rb_obj_as_string(str);
     enc = rb_enc_get(ptr->string);
@@ -1194,6 +1193,7 @@ strio_write(VALUE self, VALUE str)
 	OBJ_INFECT(ptr->string, str);
     }
     OBJ_INFECT(ptr->string, self);
+    RB_GC_GUARD(str);
     ptr->pos += len;
     return LONG2NUM(len);
 }