Fix creation of filegroups in collection
Fix for a bug found in 0.7.7. Steps to reproduce:
int snippet() {
TGrid::Connect("alien://");
TString command = "find -l 1 -o 0 /alice/sim/2022/LHC22d1c2//295671 */galice.root";
TString file = "wn.xml";
Int_t stage = 1;
gGrid->Command(command);
gGrid->Stdout(); // so far so good
TGridCollection *tmp = gGrid->OpenCollectionQuery(gGrid->Command(command),kTRUE);
tmp->ExportXML(Form("file://__tmp%d__%s", stage, file.Data()), kFALSE, kFALSE, command.Data());
return 0;
}