patch 8.2.0168: Coverity warning for assigning NULL to an option

Problem:    Coverity warning for assigning NULL to an option.
Solution:   Use empty string instead of NULL.

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    168,
 /**/
     167,
 /**/