linter: report it as an error when running the linting program fails

When something goes wrong, nano should beep and the status bar should
use the error color (red by default).

This fixes https://savannah.gnu.org/bugs/?57116.

src/text.c

@@ -2890,7 +2890,7 @@ void do_linter(void)
 	waitpid(pid_lint, &lint_status, 0);
 
 	if (!WIFEXITED(lint_status) || WEXITSTATUS(lint_status) > 2) {
-		statusbar(invocation_error(openfile->syntax->linter));
+		statusline(ALERT, _("Error invoking '%s'"), openfile->syntax->linter);
 		return;
 	}