CtAccumulation does not free buffer (until prepared again)

On BM18 with the iris camera. The issue can be reproduced by interleaving SINGLE and ACCUMULATION acquisitions:

limatake(0.035, 10000, det3, image_flip=[False, True])

limatake(0.175, 10000, det3, save=False, acq_mode="ACCUMULATION", acc_max_expo_time=0.035, acc_out_type = "Bpp16", acc_operation = "ACC_MEAN", image_flip=[False, True])

The memory allocated is not properly freed after the ACCUMULATION scan. A subsequent scan in SINGLE mode will be killed by the OOM killer.

The m_datas queue that keeps a reference on the data after accumulation is cleared during the preparation of the next ACCUMULATION acquisition, but if the next acquisition is SINGLE, it is not cleared, then the device try to allocate more memory than available.

cc: @muzelle