segfault fixed

When using both -J and a single -O with multiple URLs, a missing init
could cause badness.

Bug: http://curl.haxx.se/mail/lib-2011-07/0126.html and
     http://bugzilla.redhat.com/723075
Reported by: Paul Howarth and Garrett Holmstrom

src/main.c

@@ -4898,6 +4898,7 @@ operate(struct Configurable *config, int argc, argv_item_t argv[])
     outs.stream = stdout;
     outs.config = config;
     outs.bytes = 0; /* nothing written yet */
+    outs.filename = NULL;
 
     /* save outfile pattern before expansion */
     if(urlnode->outfile) {