Merge pull request #154 in ZP/z-push from bugfix/ZP-840-ping-loop-if-exporter-state-is-not to develop

* commit 'a1541482':
  ZP-840 Rename exception variable.
  ZP-840 Renamed exception variable.
  ZP-840 Catch StateInvalidException when in partial mode.
  ZP-840 Do not throw StateNotFoundException as this messes up Ping. Just treat it as StateInvalid (which is true, FD indicates a state that is not available), do not catch both types in Ping as only StateInvalidException will be thrown.

(cherry picked from commit abf4c77c)

Conflicts:
	src/lib/core/synccollections.php
	src/lib/request/ping.php