patch 8.1.0495: :filter only supports some commands

Problem:    :filter only supports some commands.
Solution:   Add :filter support for more commands. (Marcin Szamotulski,
            closes #2856)
diff --git a/src/userfunc.c b/src/userfunc.c
index ec239c7..7c3b7f6 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -1882,6 +1882,8 @@
 		{
 		    --todo;
 		    fp = HI2UF(hi);
+		    if (message_filtered(fp->uf_name))
+			continue;
 		    if (!func_name_refcount(fp->uf_name))
 			list_func_head(fp, FALSE);
 		}