patch 8.2.3972: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move the last errors from globals.h to errors.h.
diff --git a/src/popupmenu.c b/src/popupmenu.c
index 86a9cbb..cf5558b 100644
--- a/src/popupmenu.c
+++ b/src/popupmenu.c
@@ -1476,7 +1476,7 @@
     // pum_size being zero.
     if (pum_size <= 0)
     {
-	emsg(e_menuothermode);
+	emsg(e_menu_only_exists_in_another_mode);
 	return;
     }