Fix parsing of single element scale range #753

Job	Run time
build-vegafusion-wasm	7m 15s
test-rust (ubuntu-20.04)	7m 18s
test-rust (windows-2022)	7m 3s
test-rust (macos-11)	1s
build-vegafusion-jupyter-packages	7m 17s
build-vegafusion-packages	2m 5s
build-vegafusion-python-embed-linux-64	7m 52s
build-vegafusion-python-embed-linux-arm64	8m 3s
build-vegafusion-python-embed-osx-64	7m 15s
build-vegafusion-python-embed-osx-arm64	7m 14s
build-vegafusion-python-embed-win-64	5m 53s
build-vegafusion-server-linux-64	7m 14s
build-vegafusion-server-linux-arm64	8m 16s
build-vegafusion-server-osx-64	1s
build-vegafusion-server-osx-arm64	7m 14s
build-vegafusion-server-win-64	7m 4s
check-rust	7m 14s
test-vegafusion-python-win-64	1s
test-vegafusion-python-osx-64	1s
test-vegafusion-jupyter-linux-64	1s
test-vegafusion-python-linux-64	1s
	1h 44m 23s

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