fix compile warning and segfault caused by a missing return statement

we had the following compile warning:
prt-get.cpp: In member function 'virtual SignalHandler::HandlerResult PrtGet::handleSignal(int)':
prtget.cpp:1628:1: warning: no return statement in function returning non-void [-Wreturn-type] }

which leads to a segfault if we compile prt-get with optimalization, e.g. -O2,
and interrupt prt-get with ^C

src/prtget.cpp

@@ -1628,6 +1628,8 @@ SignalHandler::HandlerResult PrtGet::handleSignal( int signal )
     if ( m_currentTransaction ) {
         evaluateResult( *m_currentTransaction, false, true );
     }
+
+    return EXIT;
 }
 
 /*!