patch 8.1.0019: error when defining a Lambda with index of a function result

Problem:    Error when defining a Lambda with index of a function result.
Solution:   When not evaluating an expression and skipping a function call,
            set the return value to VAR_UNKNOWN.

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    19,
 /**/
     18,
 /**/