Prevent infinite loop on zero length USB descriptors

If a USB device descriptor has zero length it is invalid and iteration
should stop otherwise the code iterating will go into an infinite loop.

Bug: 149986186
Test: attach bad USB device with invalid descriptor length 0 then attach
a good USB device and ensure it is recognized properly

Change-Id: I7571a6357bdc13af221cf8be01eba16f5bc976a3