Fix supervision when no child filbers are active (#164)

* Fix supervision when no child filbers are active

* Fix callback reference

Author: natefaubion

src/Effect/Aff.js

@@ -169,6 +169,10 @@ var Aff = function () {
       },
       killAll: function (killError, cb) {
         return function () {
+          if (count === 0) {
+            return cb();
+          }
+
           var killCount = 0;
           var kills     = {};
 

test/Test/Main.purs

@@ -667,6 +667,14 @@ test_regression_kill_sync_async = assert "regression/kill-sync-async" do
   killFiber (error "Nope.") f1
   pure true
 
+test_regression_kill_empty_supervisor ∷ Aff Unit
+test_regression_kill_empty_supervisor = assert "regression/kill-empty-supervisor" do
+  f1 ← forkAff $ supervise $ delay $ Milliseconds 10.0
+  let
+    a = parallel $ killFiber (error "Nope.") f1 $> true
+    b = parallel $ delay (Milliseconds 20.0) $> false
+  sequential (a <|> b)
+
 main ∷ Effect Unit
 main = do
   test_pure
@@ -715,3 +723,4 @@ main = do
     test_regression_par_apply_async_canceler
     test_regression_bracket_catch_cleanup
     test_regression_kill_sync_async
+    test_regression_kill_empty_supervisor