[openAcquisition] Coerce 0 to 1 instead of throwing exception.
[openAcquisition] Coerce 0 to 1 instead of throwing exception.

This should be more backwards-compatible with old scripts -- not to mention
the old openAcquisition() that doesn't take a positions parameter calls the
new one with a 0 for nrPositions! So now that won't throw an exception.

git-svn-id: 03a8048b5ee8463be5048a3801110fb50f378627@15024 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd

kmdouglass/Micro-Manager,kmdouglass/Micro-Manager