HPCC-22126 Potential roxie crash in CRoxieLateStartActivity::stop

User reported a core in this function when using a library.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>

roxie/ccd/ccdserver.cpp

@@ -1716,7 +1716,7 @@ public:
     }
     virtual void stop()
     {
-        if (!prefiltered)
+        if (!prefiltered && inputStream)
         {
             inputStream->stop();
         }