patch 8.2.3970: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 0be4503..636dd38 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -2641,8 +2641,8 @@
 	return e_invalid_in_cmdline_window;
 #endif
     if (textwinlock != 0)
-	return e_textwinlock;
-    return e_textlock;
+	return e_not_allowed_to_change_text_or_change_window;
+    return e_not_allowed_to_change_text_here;
 }
 
 /*