set buffer_frame_count_ before setting up callback

[bjudkewitz]

I am not entirely sure if the new frame callback exists in a different thread, but just to be sure I would move these two lines further up, at least above pl_exp_start_cont which I believe starts camera acquisition.

PyVCAM/src/pyvcam/pvcmodule.cpp

Lines 720 to 721 in 06f7eee

	camInstance.buffer_frame_count_ = buffer_frame_count;
	camInstance.setAcquisitiontMode(false);