Pull up following revision(s) (requested by mlelstv in ticket #590):

sys/dev/usb/uvideo.c: revision 1.50
sys/dev/usb/uvideo.c: revision 1.51
sys/dev/usb/uvideo.c: revision 1.52

Avoid kmem_alloc(0,..), which hits an assertion.

PR kern/53734: Prevent kernel panic during Wide Vision FHD Camera detection
Check if size is zero, too.

PR kern/53734
we want to check that the allocation is going to be zero, not whether
some pointer is NULL (oops).

Should be the right version this time!

(martin)