patch 8.2.3830: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/ui.c b/src/ui.c
index 8cbe49b..db49cc8 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -577,7 +577,7 @@
 suspend_shell(void)
 {
     if (*p_sh == NUL)
-	emsg(_(e_shellempty));
+	emsg(_(e_shell_option_is_empty));
     else
     {
 	msg_puts(_("new shell started\n"));