Addresses coding convention issues in the DevicePathLib
Should not cause any compatibility issues with any existing modules.
Adds ASSERT() checks for NULL device path nodes passed into these functions.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@7445 6f19259b-4bc3-4df7-8a09-765794883524