Fix a bug on RecordRewriter when a variable is matched in many clauses, closes #1037

Author: José Valim

lib/elixir/lib/kernel/record_rewriter.ex

@@ -363,6 +363,8 @@ defmodule Kernel.RecordRewriter do
           { :ok, _ } -> :orddict.store(key, nil, acc)
           :error -> :orddict.erase(key, acc)
         end
+      { key, nil }, acc ->
+        :orddict.store(key, nil, acc)
     end
 
     join_dict(t, other)

lib/elixir/test/elixir/kernel/record_rewriter_test.exs

@@ -159,6 +159,9 @@ defmodule Kernel.RecordRewriterTest do
 
     clause = clause(fn -> case something do 1 -> x = Macro.Env[]; 2 -> x = Range[] end end)
     assert optimize_clause(clause) == { clause, [x: nil], nil }
+
+    clause = clause(fn -> case something do x = Macro.Env[] -> x; x = Range[] -> x; _ -> :ok end end)
+    assert optimize_clause(clause) == { clause, [x: nil], nil }
   end
 
   test "inside case with nested tuple" do