Fix user mapping when variables aren't given.

@@ -25,7 +25,7 @@ adjust_tool_uid_gid() {
 			usermod_args+=(-aG "${new_groups[*]}")
 		fi
 	fi
-	if [[ ${#usermod_args[*]} ]]; then
+	if [[ ${#usermod_args[*]} -gt 0 ]]; then
 		usermod "${usermod_args[@]}" tool
 	fi
 }