Do not fail if path is not set on the file source

It may be set on the atom instead.

handler_file.go

@@ -2,7 +2,6 @@ package tabacco
 
 import (
 	"context"
-	"errors"
 	"path/filepath"
 
 	"git.autistici.org/ai3/tools/tabacco/jobs"
@@ -13,11 +12,7 @@ type fileHandler struct {
 }
 
 func newFileHandler(name string, params Params) (Handler, error) {
-	path := params.Get("path")
-	if path == "" {
-		return nil, errors.New("path not set")
-	}
-	return &fileHandler{path: path}, nil
+	return &fileHandler{path: params.Get("path")}, nil
 }
 
 // Convert the atom to a path.