patch 8.1.1512: ch_evalexpr() hangs when used recursively

Problem:    ch_evalexpr() hangs when used recursively. (Paul Jolly)
Solution:   Change ch_block_id from a single number to a list of IDs to wait
            on.

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1512,
 /**/
     1511,
 /**/