Check by @v before converting the entry on expired?

We should convert when @v is defined not @value.

The test was calling value first that already converts the entry so we
are not catching this bug.

activesupport/lib/active_support/cache.rb

@@ -593,7 +593,7 @@ def value
       # Check if the entry is expired. The +expires_in+ parameter can override
       # the value set when the entry was created.
       def expired?
-        convert_version_4beta1_entry! if defined?(@value)
+        convert_version_4beta1_entry! if defined?(@v)
         @expires_in && @created_at + @expires_in <= Time.now.to_f
       end
 

activesupport/test/caching_test.rb

@@ -1001,7 +1001,7 @@ def test_restoring_expired_version_4beta1_entries
     version_4beta1_entry.instance_variable_set(:@v, "hello")
     version_4beta1_entry.instance_variable_set(:@x, Time.now.to_i - 1)
     entry = Marshal.load(Marshal.dump(version_4beta1_entry))
-    assert_equal "hello", entry.value
     assert_equal true, entry.expired?
+    assert_equal "hello", entry.value
   end
 end