Small fix that clears errors on sites with mupltiple contexts. Sometimes
array $modx->contexts get wrong key=>object assigment cause of switchContext
don't fill $this->contexts array, but links it to $this->context.

Signed-off-by: Indomian <blade39@yandex.ru>
[#9524] changelog entry
[#9524] Fix invalid context assignment in modX::switchContext()

Merge branch 'bug-9524' into release-2.2

* bug-9524:
  [#9524] changelog entry
  Small fix that clears errors on sites with mupltiple contexts. Sometimes array $modx->contexts get wrong key=>object assigment cause of switchContext don't fill $this->contexts array, but links it to $this->context.