[JS] Fix Parser.getSourceName returning undefined #1043

Job	Run time
cpp-lib-build (macos-11, clang, ON)	7m 44s
cpp-lib-build (macos-11, clang, OFF)	8m 21s
build (macos-11, tool)	1m 57s
cpp-lib-build (macos-11, gcc, ON)	9m 26s
build (macos-11, cpp)	8m 33s
cpp-lib-build (macos-11, gcc, OFF)	9m 39s
build (macos-11, csharp)	9m 35s
cpp-lib-build (ubuntu-20.04, clang, ON)	3m 13s
build (macos-11, dart)	6m 3s
cpp-lib-build (ubuntu-20.04, clang, OFF)	3m 28s
build (macos-11, go)	5m 8s
cpp-lib-build (ubuntu-20.04, gcc, ON)	4m 23s
build (macos-11, java)	2m 6s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	4m 44s
build (macos-11, javascript)	2m 40s
cpp-lib-build (windows-2022, clang, ON)	4m 39s
build (macos-11, typescript)	18m 26s
cpp-lib-build (windows-2022, clang, OFF)	5m 19s
build (macos-11, php)	24s
cpp-lib-build (windows-2022, cl)	4m 26s
build (macos-11, python3)	1m 55s
build (ubuntu-20.04, tool)	58s
build (ubuntu-20.04, cpp)	17m 4s
build (ubuntu-20.04, csharp)	4m 53s
build (ubuntu-20.04, dart)	3m 45s
build (ubuntu-20.04, go)	2m 16s
build (ubuntu-20.04, java)	1m 4s
build (ubuntu-20.04, javascript)	1m 42s
build (ubuntu-20.04, typescript)	9m 49s
build (ubuntu-20.04, php)	1m 22s
build (ubuntu-20.04, python3)	1m 25s
build (windows-2022, tool)	1m 39s
build (windows-2022, cpp)	22m 25s
build (windows-2022, csharp)	6m 43s
build (windows-2022, dart)	4m 24s
build (windows-2022, go)	5m 45s
build (windows-2022, java)	1m 54s
build (windows-2022, javascript)	2m 26s
build (windows-2022, typescript)	22m 59s
build (windows-2022, php)	3m 23s
build (windows-2022, python3)	1m 46s
	3h 59m 51s

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