Fix null pointer dereference in ipc_boostrap

ipc/ipc_mojo_bootstrap.cc

Index: ipc/ipc_mojo_bootstrap.cc
diff --git a/ipc/ipc_mojo_bootstrap.cc b/ipc/ipc_mojo_bootstrap.cc
index 2c554620e9d67b25c437202929b494397cfd2167..89a74343f811b89c5f4bc243814912aaab8c29fb 100644
--- a/ipc/ipc_mojo_bootstrap.cc
+++ b/ipc/ipc_mojo_bootstrap.cc
@@ -788,6 +788,12 @@ class ChannelAssociatedGroupController
     if (!endpoint)
       return;
 
+    // Careful, if the endpoint is detached its members are cleared. Check for
+    // that before dereferencing.
+    mojo::InterfaceEndpointClient* client = endpoint->client();
+    if (!client)
+      return;
+
     DCHECK(endpoint->task_runner()->BelongsToCurrentThread());
     MessageWrapper message_wrapper = endpoint->PopSyncMessage(message_id);
 
@@ -796,10 +802,6 @@ class ChannelAssociatedGroupController
     if (message_wrapper.value().IsNull())
       return;
 
-    mojo::InterfaceEndpointClient* client = endpoint->client();
-    if (!client)
-      return;
-
     bool result = false;
     {
       base::AutoUnlock unlocker(lock_);