Add a simple file isopened guard

The saga of why the docker container fails QA continues

qa/tests/spice/test_netlist_exporter_spice.h

@@ -117,6 +117,7 @@ public:
         wxFFile file( GetNetlistPath( true ), "rt" );
         wxString netlist;
 
+        BOOST_REQUIRE( file.IsOpened() );
         file.ReadAll( &netlist );
 
         //ngspice->Init();