patch 9.1.0973: too many strlen() calls in fileio.c

Problem:  too many strlen() calls in fileio.c
Solution: refactor fileio.c and remove calls to STRLEN(),
          check for out-of-memory condition in buf_check_timestamp()
          (John Marriott)

closes: #16306

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    973,
 /**/
     972,
 /**/