string.c: assertion

* string.c (str_shared_replace): use RUBY_ASSERT for
  pre-condition.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57628 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

string.c

@@ -1323,7 +1323,7 @@ str_shared_replace(VALUE str, VALUE str2)
     int cr;
     int termlen;
 
-    ASSUME(str2 != str);
+    RUBY_ASSERT(str2 != str);
     enc = STR_ENC_GET(str2);
     cr = ENC_CODERANGE(str2);
     str_discard(str);