Merge pull request #1499 from jtattermusch/core_cb_fix

Fix server side call finalization when connection is closed.

src/core/transport/chttp2_transport.c

@@ -823,12 +823,13 @@ static void unlock(transport *t) {
   finish_reads(t);
 
   /* gather any callbacks that need to be made */
-  if (!t->calling_back && cb) {
+  if (!t->calling_back) {
     perform_callbacks = prepare_callbacks(t);
     if (perform_callbacks) {
       t->calling_back = 1;
     }
-    if (t->error_state == ERROR_STATE_SEEN && !t->writing) {
+    if (cb) {
+      if (t->error_state == ERROR_STATE_SEEN && !t->writing && !t->calling_back) {
         call_closed = 1;
         t->calling_back = 1;
         t->cb = NULL; /* no more callbacks */
@@ -843,6 +844,7 @@ static void unlock(transport *t) {
         t->calling_back = 1;
       }
     }
+  }
 
   if (perform_callbacks || call_closed || num_goaways) {
     ref_transport(t);