Handle ZIP files with padding in the extra fields

Handle ZIP files with padding in the extra fields

Some ZIP files (certain android AAR packages) include ZIP extra fields
that appear to be padded with 0s. This is technically incorrect, however
other ZIP implementations appear to deal with these type of technically
malformed files. It appears that these broken implementations may be
padding the field to end on a word-aligned boundary.

Instead of generating an error if the length of the extra field is less
than the minimum size (4 bytes), consume the 1 - 3 bytes while checking that
each byte is zero. If all bytes are zero, no error is raised.