patch 8.1.0318: the getftype() test may fail for char devices

Problem:    The getftype() test may fail for char devices if the file
            disappeared in between the listing and the getftype() call.
Solution:   Ignore empty result. (Ozaki Kiichi, closes #3360)

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    318,
 /**/
     317,
 /**/