fix mem leak in rb_file_s_readlink() (ruby-core:394)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@2777 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

file.c

@@ -1301,7 +1301,10 @@ rb_file_s_readlink(klass, path)
 	size *= 2;
 	buf = xrealloc(buf, size);
     }
-    if (rv < 0) rb_sys_fail(RSTRING(path)->ptr);
+    if (rv < 0) {
+	free(buf);
+	rb_sys_fail(RSTRING(path)->ptr);
+    }
     v = rb_tainted_str_new(buf, rv);
     free(buf);