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)
diff --git a/src/version.c b/src/version.c
index d599381..1afe230 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    318,
+/**/
     317,
 /**/
     316,