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/bufwrite.c b/src/bufwrite.c
index a7e1ad5..7cf5724 100644
--- a/src/bufwrite.c
+++ b/src/bufwrite.c
@@ -700,7 +700,7 @@
     {
 	// This can happen during startup when there is a stray "w" in the
 	// vimrc file.
-	emsg(_(e_emptybuf));
+	emsg(_(e_empty_buffer));
 	return FAIL;
     }