io.c: buffer must be modifiable

* io.c (io_setstrbuf): always check if the buffer is modifiable.
  [ruby-core:62643] [Bug #9847]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45979 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/io.c b/io.c
index 533989cb62..5499086448 100644
--- a/io.c
+++ b/io.c
@@ -2370,8 +2370,8 @@ io_setstrbuf(VALUE *str, long len)
 	VALUE s = StringValue(*str);
 	long clen = RSTRING_LEN(s);
 	if (clen >= len) {
+	    rb_str_modify(s);
 	    if (clen != len) {
-		rb_str_modify(s);
 		rb_str_set_len(s, len);
 	    }
 	    return;