Exit callback 'response_network_stream_read_data_cb' if client_io is null
Related to this WebKit bug:
https://bugs.webkit.org/show_bug.cgi?id=225637
It seems sometimes the 'response_network_stream_read_data_cb' callback gets called with value 'count=1', but 'client_io' is null. Reading the stacktrace it looks this might be triggered by libsoup/soup-connection.c:961, which attempts to read 1 byte to check whether the socket is readable.
I haven't tested this patch.