- web: avoid error if subscribed user doesn't exist

fixed #753


svn path=/trunk/boinc/; revision=16191

checkin_notes

@@ -8299,3 +8299,9 @@ David  10 Oct 2008
         http_curl.cpp
     html/user/
         forum_post.php
+
+David  12 Oct 2008
+    - web: avoid error if subscribed user doesn't exist
+
+    html/inc/
+        forum.inc

html/inc/forum.inc

@@ -775,7 +775,9 @@ function create_post($content, $parent_id, $user, $forum, $thread, $signature) {
     foreach ($subs as $sub) {
         if ($user->id == $sub->userid) continue;
         $user2 = BoincUser::lookup_id($sub->userid);
-        notify_subscriber($thread, $user2);
+        if ($user2) {
+            notify_subscriber($thread, $user2);
+        }
     }
     $user->update("posts=posts+1");
     $thread->update("replies=replies+1, timestamp=$now");