file modes in top-level ar archive don't match dpkg

[programmerjake]

first bytes in a .deb created by dpkg:

!<arch>
debian-binary   1611345884  0     0     100644  4         `
2.0
control.tar.xz  1611345884  0     0     100644  10384     `

first bytes in a .deb created by cargo-deb:

!<arch>
debian-binary   1712732414  0     0     644     4         `
2.0
control.tar.gz  1712732414  0     0     644     1435      `

notice how the dpkg version has mode 100644, where the initial 10 indicates that they're files:
https://unix.stackexchange.com/questions/450480/file-permission-with-six-octal-digits-in-git-what-does-it-mean/450488#450488

I encountered this while trying to figure out why file-roller couldn't extract the control.tar.gz or data.tar.gz files...

[kornelski]

Please make a PR with a fix.