fix #4855

Auditors: @bbondy

Test Plan:
1. Open "about:autofill"
2. Click "Add Address"
3. The save button should be disabled
4. Enter the detail of form, the save button should be enabled
5. Remove all detail of form, the save button should be disabled

1. Open "about:autofill"
2. Click "Add Credit Card"
3. The save button should be disabled
4. Enter the detail of form, the save button should be enabled (Name, Card Number)
5. Remove all detail of form, the save button should be disabled (Name, Card Number)

1. Open "about:autofill"
2. Add address entry
3. Edit the address entry
4. Remove all detail of form, the save button should be disabled

1. Open "about:autofill"
2. Add credit card entry
3. Edit the credit card entry
4. Remove all detail of form, the save button should be disabled (Name, Card Number)