Fix invalid platforms in main. (#39)

Ensure `pylama` is run in the poetry env:
* .pre-commit-config.yaml : Set pylama `entry` to `poetry run pylama`.

Fix invalid platforms in `main`.
* req2flatpak.py: Handle the case where PlatformFactory might return `None` if a platform could not be passed. 

Authored-by: real-yfprojects <real-yfprojects@users.noreply.github.com>

.pre-commit-config.yaml

@@ -41,7 +41,7 @@ repos:
     hooks:
       - id: pylama
         name: pylama
-        entry: pylama
+        entry: poetry run pylama
         language: system
         types: [python]
 

req2flatpak.py

@@ -766,6 +766,7 @@ def main():
         DownloadChooser.wheel_or_sdist(release, platform)
         for release in releases
         for platform in platforms
+        if platform
     }
 
     # generate flatpak-builder build module