[mediacapture-depth] Need an invalid value

fluffy has just created a new issue for 
https://github.com/w3c/mediacapture-depth:

== Need an invalid value  ==
This bug is important to fix before this goes for wider review. 

Most depth sensors may not product a depth for every pixel. It is 
important that when they can no detect what the depth value is at a 
give location, they can report that there is no reading vs reporting a
 bad reading. We need to define a way a value that indicates "no depth
 detected". Typically this is zero. Once we define this value, then 
the near / far distance calculations formulas need to be adjusted. 

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-depth/issues/137 using your GitHub
 account