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/buffer.c b/src/buffer.c
index c5b273c..c00993a 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1608,7 +1608,7 @@
 	if (addr_count == 2)
 	{
 	    if (*arg)		// both range and argument is not allowed
-		return ex_errmsg(e_trailing_arg, arg);
+		return ex_errmsg(e_trailing_characters_str, arg);
 	    bnr = start_bnr;
 	}
 	else	// addr_count == 1