[TDF] Fix ctor with single filename as string.
[TDF] Fix ctor with single filename as string.

Fixes ROOT-9037.

olifre/root,zzxuanyuan/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,zzxuanyuan/root,root-mirror/root,karies/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,zzxuanyuan/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,karies/root,root-mirror/root,karies/root,olifre/root,zzxuanyuan/root,karies/root,zzxuanyuan/root,olifre/root,zzxuanyuan/root,karies/root,olifre/root,zzxuanyuan/root,karies/root,root-mirror/root,karies/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,root-mirror/root,karies/root,karies/root,root-mirror/root