patch 8.1.2180: Error E303 is not useful when 'directory' is empty

Problem:    Error E303 is not useful when 'directory' is empty.
Solution:   Skip the error message. (Daniel Hahler, #5067)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 34fb484..8436c8a 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2693,7 +2693,7 @@
 	- The swap file will be created in the first directory where this is
 	  possible.
 	- Empty means that no swap file will be used (recovery is
-	  impossible!).
+	  impossible!) and no |E303| error will be given.
 	- A directory "." means to put the swap file in the same directory as
 	  the edited file.  On Unix, a dot is prepended to the file name, so
 	  it doesn't show in a directory listing.  On MS-Windows the "hidden"