Previously pkglistgen.py assumed that a project either used product-builder or the new product-composer, by exiting unrecoverably when a *.productcompose.in file was found but the relative 000productcompose directory was absent. This is not the case for SL Micro as the shared SLFO codebase is still an hybrid OBS/git project and hence its stagings are not git based and can't use product composer. This patch was tested for the SUSE:ALP:Source:Standard:1.0:Staging:A and SUSE:ALP:Products:Marble:6.0 projects (together with https://github.com/openSUSE/openSUSE-release-tools/pull/3078). Instead of raising an exception when the 000productcompose directory is not found it makes a log stating that product-composer will be skipped.