[filebrowser] Update xxd_test to not fail for different offset lengths

Some distributions have different implementations of xxd which change how many bytes are outputted for the offset field. The current xxd_test.py assumes that this is the same as the hue xxd implementation (which is 7bytes of offset). It would be better to not care about leading zeros in the test which would make this test extendable to all distributions. This will not affect the other bytes being outputted and will still compare both outputs once the padding is removed.