config: Ignore empty lines to avoid OOB array access

Fixes T187

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/config.c

@@ -521,6 +521,11 @@ ssh_config_parse_line(ssh_session session,
   long l;
   int64_t ll;
 
+  /* Ignore empty lines */
+  if (line == NULL || *line == '\0') {
+    return 0;
+  }
+
   x = s = strdup(line);
   if (s == NULL) {
     ssh_set_error_oom(session);