patch 8.1.0169: calling message_filtered() a bit too often

Problem:    Calling message_filtered() a bit too often.
Solution:   Only call message_filtered() when filtering is already false.
diff --git a/runtime/doc/quickfix.txt b/runtime/doc/quickfix.txt
index c3f8504..2955eda 100644
--- a/runtime/doc/quickfix.txt
+++ b/runtime/doc/quickfix.txt
@@ -298,6 +298,10 @@
 			from the last error backwards, -1 being the last error.
 			The 'switchbuf' settings are respected when jumping
 			to a buffer.
+			The |:filter| command can be used to display only the
+			quickfix entries matching a supplied pattern. The
+			pattern is matched against the filename, module name,
+			pattern and text of the entry.
 
 :cl[ist] +{count}	List the current and next {count} valid errors.  This
 			is similar to ":clist from from+count", where "from"
@@ -1287,7 +1291,7 @@
 Changing directory
 
 The following uppercase conversion characters specify the type of special
-format strings.  At most one of them may be given as a prefix at the begin
+format strings.  At most one of them may be given as a prefix at the beginning
 of a single comma-separated format pattern.
 Some compilers produce messages that consist of directory names that have to
 be prepended to each file name read by %f (example: GNU make).  The following