Fix the first captured image being dropped
Fix the first captured image being dropped

The first frame generated by any camera was always lost in the libuvc
layer, and not passed on to the listening application.

The start value of seq (thus hold_seq) could be arbitrary, but it must
be non-zero.  Both the callback listener and the polling function's
last_seq / last_polled_seq start initialised to zero, which causes any
image with hold_seq zero to be ignored.

ktossell/libuvc,ktossell/libuvc