patch 8.2.3750: error messages are everywhere

Problem:    Error messages are everywhere.
Solution:   Move more error messages to errors.h and adjust the names.
diff --git a/src/register.c b/src/register.c
index d225d77..6a4bc2c 100644
--- a/src/register.c
+++ b/src/register.c
@@ -2836,7 +2836,7 @@
 
 	    buf = buflist_findnr(num);
 	    if (buf == NULL)
-		semsg(_(e_nobufnr), (long)num);
+		semsg(_(e_buffer_nr_does_not_exist), (long)num);
 	}
 	else
 	    buf = buflist_findnr(buflist_findpat(str, str + STRLEN(str),