Fix array initialization trick

Author: sjakobi

Data/HashMap/Internal.hs

@@ -2310,7 +2310,7 @@ updateOrConcatWithKey :: Eq k => (k -> v -> v -> (# v #)) -> A.Array (Leaf k v)
 updateOrConcatWithKey f ary1 ary2 = A.run $ do
     let n1 = A.length ary1
     let n2 = A.length ary2
-    mary <- A.new (n1 + n2) (A.index ary1 1)
+    mary <- A.new (n1 + n2) (A.index ary1 0)
     -- copy over all elements from ary1
     A.copy ary1 1 mary 1 (n1-1)
     -- append or update all elements from ary2