Fix UAF in caRepeaterThread

The ca_repeater function has some failure cases which can cause it to
return. In such a situation, a reference to the current thread's
epicsThreadId is kept in the taskwd, causing an eventual use-after-free
when the taskwd tries to determine the task's status.

We fix this problem by removing the thread from the taskwd if
ca_repeater ever returns.

modules/ca/src/client/repeater.cpp

@@ -645,6 +645,7 @@ extern "C" void caRepeaterThread ( void * /* pDummy */ )
 {
     taskwdInsert ( epicsThreadGetIdSelf(), NULL, NULL );
     ca_repeater ();
+    taskwdRemove ( 0 );
 }