gnulib-tool.py: Filter out dependencies that cannot be found. Reported by Paul Eggert in <https://lists.gnu.org/archive/html/bug-gnulib/2024-05/msg00136.html>. * pygnulib/GLModuleSystem.py (GLModule.getDependenciesWithConditions): Reorder conditionals to avoid duplicate checks. Filter out None from the gathered dependencies when gathering module dependencies. Let GLModuleSystem.find() warn instead of crashing.