update: handle large, corrupt, or inaccessible fastlane/triple-t files

```
Traceback (most recent call last):
  File "../fdroid", line 22, in <module>
    fdroidserver.__main__.main()
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/__main__.py", line 227, in main
    raise e
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/__main__.py", line 208, in main
    mod.main()
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/update.py", line 2340, in main
    repoapps = prepare_apps(apps, apks, repodirs[0])
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/update.py", line 2176, in prepare_apps
    copy_triple_t_store_metadata(apps_with_packages)
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/update.py", line 1076, in copy_triple_t_store_metadata
    _set_author_entry(app, 'authorWebSite', os.path.join(root, f))
  File "/var/lib/jenkins/userContent/reproducible/reproducible_fdroid_build_apps/fdroidserver/update.py", line 784, in _set_author_entry
    with open(f, errors='replace') as fp:
FileNotFoundError: [Errno 2] No such file or directory: 'build/player.efis.cfd/pfd/src/main/play/contact-website.txt'
```