Comment 4 for bug 1766391

There are two parts to this bug.
- in some cases, at the time shim-signed's postinst runs, there may be linux-image packages installed for which one or more dkms modules are not currently built. There are a number of legitimate reasons why this may be the case, including unpack ordering during an upgrade. shim-signed needs to gracefully handle the possibility that 'dkms uninstall' fails because the module is not installed.
- the refactoring of the kernel packaging that landed in 4.15.0-19-generic has a typo that prevents it from triggering dkms builds on installation. The correct directory name is /etc/kernel/header_postinst.d/; /var/lib/dpkg/info/linux-headers-4.15.0-19-generic.postinst references /etc/kernel/headers_postinst.d which does not exist.