patch 8.2.3291: Coverity warns for not checking return value

Problem:    Coverity warns for not checking return value.
Solution:   If dict_add() fails give an error message.

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3291,
 /**/
     3290,
 /**/