patch 8.2.0208: fnamemodify() does not apply ":~" when followed by ":."

Problem:    Fnamemodify() does not apply ":~" when followed by ":.".
Solution:   Don't let a failing ":." cause the ":~" to be skipped. (Yasuhiro
            Matsumoto, closes #5577)
diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index c4638b6..5289756 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -933,8 +933,7 @@
 		directory.
 	:.	Reduce file name to be relative to current directory, if
 		possible.  File name is unmodified if it is not below the
-		current directory, but on MS-Windows the drive is removed if
-		it is the current drive.
+		current directory.
 		For maximum shortness, use ":~:.".
 	:h	Head of the file name (the last component and any separators
 		removed).  Cannot be used with :e, :r or :t.