EffectBundle: check nb channels to write speaker angles

When speaker angles are queried, the size of the array for the
  returned data is 3x the number of channels (where really it
  should be max(2, nbChannels)). The code assumed it was at
  least 3x2 (where 2 is the number of virtual speakers this
  effect supports) and would thus crash when called for a mono
  channel mask.

Test: see repro steps in bug
Bug: 32591350
Change-Id: I33d4bff6b2e19a9fc4284a85a446804878d3a410