ringaccount: fix non-handled exception

RingAccount::handlePendingCall may throw exception and was not
catched by the handlePendingCallList loop.
This leds to non-handled pending calls (all after the failing one).

This patch fixes that by catch all exception and drop bad guys.

Change-Id: Ic62e115bf32b467e04a19f2ae077d8256a69d90e
Tuleap: #106