HPCC-11288 - regression if inside transaction

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>

plugins/fileservices/fileservices.cpp

@@ -1170,6 +1170,8 @@ public:
             transaction = _transaction;
             transaction->start();
         }
+        else
+            transaction = NULL;
     }
     ~CImplicitSuperTransaction()
     {