Move the handling of unhandled exceptions in the loop.

Indeed if the UserInterface.cpp is compiled without -fno-exceptions I get:
****************** CLING ******************
* Type C++ code and press enter to run it *
*             Type .q to exit             *
*******************************************
[cling]$ throw 12;
Exception occurred. Recovering...
[cling]$ .q

So the issue is still in the build system, because I built UserInterface.cpp 'by hand'.