Slower webcams don't have an image available for the first call to capture.read(), so make sure that an image has been returned before trying to operate on a null image
Merge pull request #2 from leighpauls/master

Don't try to process a null image
Avoid busy-waiting when not getting images.

If we're waiting for a webcam to boot, it would end up in a busy loop and peg the CPU.
Merge pull request #3 from bsilver8192/master

Avoid busy-waiting when not getting images.