Fix crash when opening native / bytecode without hotreloading.

[bsansouci]

when not in hotreloading mode

[bsansouci]

Otherwise we get a unix error when trying to hotreload a file whose name is empty string here

[Schmavery]

Is it clear that we should be doing this instead of handling the empty string on the hotreloading end (and not attempting to recompile or something). I don't fully grasp the Hashtbl code right now.

cc @jaredly

[bsansouci]

Ok fixed it checking the file name. That code path was always executing anyway (the one I removed) and empty string is probably a good default anyway.

[Schmavery]

lgtm