[JS] Fix Parser.getSourceName returning undefined #1041

Job	Run time
build (macos-11, tool)	1m 59s
cpp-lib-build (macos-11, clang, ON)	7m 44s
build (macos-11, cpp)	37m 57s
cpp-lib-build (macos-11, clang, OFF)	7m 54s
build (macos-11, csharp)	10m 6s
cpp-lib-build (macos-11, gcc, ON)	8m 2s
build (macos-11, dart)	6m 18s
cpp-lib-build (macos-11, gcc, OFF)	8m 9s
build (macos-11, go)	4m 29s
cpp-lib-build (ubuntu-20.04, clang, ON)	4m 53s
build (macos-11, java)	2m 3s
cpp-lib-build (ubuntu-20.04, clang, OFF)	5m 0s
build (macos-11, javascript)	2m 32s
cpp-lib-build (ubuntu-20.04, gcc, ON)	3m 5s
build (macos-11, typescript)	18m 47s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	3m 13s
build (macos-11, php)	24s
cpp-lib-build (windows-2022, clang, ON)	4m 46s
build (macos-11, python3)	3m 4s
cpp-lib-build (windows-2022, clang, OFF)	5m 47s
build (ubuntu-20.04, tool)	59s
cpp-lib-build (windows-2022, cl)	4m 57s
build (ubuntu-20.04, cpp)	17m 42s
build (ubuntu-20.04, csharp)	5m 8s
build (ubuntu-20.04, dart)	3m 32s
build (ubuntu-20.04, go)	2m 46s
build (ubuntu-20.04, java)	1m 14s
build (ubuntu-20.04, javascript)	1m 53s
build (ubuntu-20.04, typescript)	10m 55s
build (ubuntu-20.04, php)	1m 22s
build (ubuntu-20.04, python3)	1m 2s
build (windows-2022, tool)	1m 43s
build (windows-2022, cpp)	23m 34s
build (windows-2022, csharp)	7m 40s
build (windows-2022, dart)	4m 11s
build (windows-2022, go)	6m 11s
build (windows-2022, java)	1m 50s
build (windows-2022, javascript)	2m 17s
build (windows-2022, typescript)	21m 50s
build (windows-2022, php)	2m 32s
build (windows-2022, python3)	3m 2s
	4h 32m 32s

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