Add -- to basename(1)

Otherwise, files starting with - might be interpreted by basename(1),
leading to unexpected behaviour.

slcl-upload

@@ -121,7 +121,7 @@ upload_dir()
 				--fail-with-body \
 				-b "$cookie" \
 				-F dir="$dir$src/" \
-				-F "file=@$src/$f;filename=$(basename "$f")" \
+				-F "file=@$src/$f;filename=$(basename -- "$f")" \
 				"$(escape_url "$url/upload")"
 			do
 				printf "[retrying]"