Fix regression in Exchange calendar attendee response

* During the fix of a previous late-Froyo issue, a change was made that
  appeared superficially correct, but was semantically incorrect.  This
  changed the sense of the test for whether a reply email was required
  and caused the referenced bug.
* The trivial fix is to replace the test with the (older) proper one

Bug: 2764551

Change-Id: I7c72366252cf0607aee31ee0d76aca96a7d5fc2b
1 file changed