Fix null pointer dereference when using isPropertySupported

Previously isPropertySupported methods in DeviceDriver and VideoStream would call the respective getProperty method with null pointer arguments which causes a null pointer being dereferenced (in case the property is supported).
Add missing checks for isPropertySupported to ColorStream and DepthStream
Merge pull request #39 from mherb/bugfix-property-nullptr

Fix null pointer dereference when using isPropertySupported (@mherb)