cleanup pass didn't properly handle conditionals where both branches were dead

basis/compiler/tree/cleanup/cleanup-tests.factor

@@ -500,3 +500,8 @@ cell-bits 32 = [
     [ { array-capacity } declare 1 fixnum+ ] cleaned-up-tree
     [ { [ #call? ] [ node-input-infos second literal>> 1 = ] } 1&& ] contains?
 ] unit-test
+
+[ ] [
+    [ { null } declare [ 1 ] [ 2 ] if ]
+    build-tree normalize propagate cleanup check-nodes
+] unit-test

basis/compiler/tree/cleanup/cleanup.factor

@@ -102,7 +102,7 @@ M: #declare cleanup* drop f ;
     #! If only one branch is live we don't need to branch at
     #! all; just drop the condition value.
     dup live-children sift dup length {
-        { 0 [ 2drop f ] }
+        { 0 [ drop in-d>> #drop ] }
         { 1 [ first swap in-d>> #drop prefix ] }
         [ 2drop ]
     } case ;