[MAGETWO-39185] Export UI is absent after reselecting entity type

[piotrekkaminski]

Preconditions

None

Steps to reproduce

1. Go to System -> Export in Admin Pane
2. Select for example Products entity type
3. Select "- Please Select -" option of Entity Type dropdown
4. Repeat step 2

Expected result

Export UI for Products should be shown

Actual result

Export UI not visible

[dmanners]

Issue fixed in PR #109