motis config: fix crash with no parameters #434

Job	Run time
openapi-validate	19s
formatting	47s
linux (linux-amd64-release, linux-amd64)	1m 18s
ui	36s
macos (macos-x86_64, On)	7m 15s
linux (clang-tidy)	2m 34s
macos (macos-arm64)	6m 52s
linux (linux-sanitizer)	7m 9s
linux (linux-debug, valgrind --suppressions=deps/osr/docs/tbb.supp --suppressions=deps/osr/docs/p...	8m 54s
msvc (Debug)	5m 58s
msvc (Release)	5m 6s
docker	19s
	47m 7s

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