Check frames for NULL when sending data from the renderer process using IPC

[cztomczak]

In ClientHandler::OnProcessMessageReceived any frame IDs sent as ints and then converted back into CefFrame objects need to be checked for NULL, as these frames may already be destroyed in some cases. Callbacks in the browser process like V8ContextHandler_OnContextCreated shall not be called if frame is NULL (destroyed).

Code should be analyzed whether disabling such calls won't have any side effects. Check all functions that are currently called with NULL frames. See:

cefpython/src/client_handler/client_handler.cpp

Line 28 in 824d7ce

bool ClientHandler::OnProcessMessageReceived(

Issue initially commented here:
jakogut@016f77d

Topic on the CEF forum:
https://magpcss.org/ceforum/viewtopic.php?f=6&t=16007

[cztomczak]

Fixed in commit a010e68.