Fix crash due to dangling session pointer in m_pendingInitialSession.

This happens after disconnect() kills all sessions (e.g. due to losing
internet connection while the password dialog is up, or explicit toggling
of offline/online status, or due to the "SSL not supported").

BUG: 312480, 310072, 308888, 288268, 312057, 309357, 308207, 312535, 311014, 309346, 307780
FIXED-IN: 4.10.1