patch 8.2.1794: no falsy Coalescing operator

Problem:    No falsy Coalescing operator.
Solution:   Add the "??" operator.  Fix mistake with function argument count.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1794,
 /**/
     1793,
 /**/