properly delete current channel in channel_free_list

channel_unregister() removes channels from the current smartlist while
we're in a SMORTLIST_FOREACH loop. This only works by accident.

changes/bug16924

@@ -0,0 +1,6 @@
+  o Minor bugfixes:
+    - When calling channel_free_list(), avoid calling smartlist_remove()
+      while inside a FOREACH loop. This partially reverts commit
+      17356fe7fd96af where the correct SMARTLIST_DEL_CURRENT was
+      removed.  Fixes bug 16929; bugfix on 0.2.4.4-alpha.
+

src/or/channel.c

@@ -3069,6 +3069,7 @@ channel_free_list(smartlist_t *channels, int mark_for_close)
     if (curr->cmux) {
       circuitmux_detach_all_circuits(curr->cmux, NULL);
     }
+    SMARTLIST_DEL_CURRENT(channels, curr);
     channel_unregister(curr);
     if (mark_for_close) {
       if (!CHANNEL_CONDEMNED(curr)) {