Prevent editor from closing after account is added

When the ContactEditorAccountsChangedActivity is shown (when creating
a new contact with no default account set) and a new account is added
the editor would close once an account was chosen because a new activity
instance was being created.

Test: manually verify that editor remains open after adding account
while choose account dialog is displayed

Bug 33627801

Change-Id: Icdfbceb0fc2e10619afde4fa772a2efaa21a0c5e