Crash on find-all-references on `this`

[DanielRosenwasser]

Find-all-references on this in this line in VS Code:

https://github.com/microsoft/vscode/blob/d169e9454c4f5e93cb0e9e3a33a1a12e9e38ad93/build/lib/mangle/index.ts#L31

It doesn't seem to always work - I think I had to open a workspace a level higher than the root vscode directory.

 [error] Request textDocument/references failed.
  Message: InternalError: panic handling request textDocument/references: Panics occurred during cross-project handling: [panic handling request: runtime error: slice bounds out of range [736:473]
goroutine 1919 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:26 +0x5e
github.com/microsoft/typescript-go/internal/ls.handleCrossProject[...].func2.1.1()
	github.com/microsoft/typescript-go/internal/ls/crossproject.go:89 +0x58
panic({0xca4c60?, 0xc002682678?})
	runtime/panic.go:783 +0x132
github.com/microsoft/typescript-go/internal/ls.getPossibleSymbolReferencePositions(0x0?, {0xdeffdc?, 0x4?}, 0x40bda5?)
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:1278 +0x346
github.com/microsoft/typescript-go/internal/ls.getPossibleSymbolReferenceNodes(0xc0036a5508, {0xdeffdc?, 0x0?}, 0x0?)
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:1251 +0x27
github.com/microsoft/typescript-go/internal/ls.getReferencesForThisKeyword.func2(...)
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:1142
github.com/microsoft/typescript-go/internal/core.FlatMap[...](...)
	github.com/microsoft/typescript-go/internal/core/core.go:115
github.com/microsoft/typescript-go/internal/ls.getReferencesForThisKeyword(0xc0003e0dc8, {0xc0000e7988, 0x304, 0xc004616608?})
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:1139 +0x2be
github.com/microsoft/typescript-go/internal/ls.getReferencedSymbolsSpecial(0xc0003e0dc8, {0xc0000e7988, 0x304, 0x304})
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:1081 +0x306
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getReferencedSymbolsForNode(0xc00b7a16e0, {0x10960c8, 0xc00b7a1500}, 0x5ac, 0xc0003e0dc8, 0xc000502200, {0xc0000e7988, 0x304, 0x304}, {0x0, ...})
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:968 +0x516
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).getSymbolAndEntries(0xc000330ca8?, {0x10960c8?, 0xc00b7a1500?}, 0xc007117d00?, 0xc007117cf8?, 0x4187f4?, 0x39?, 0x0?)
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:651 +0x7f
github.com/microsoft/typescript-go/internal/ls.(*LanguageService).provideSymbolsAndEntries(0xc00b7a16e0, {0x10960c8, 0xc00b7a1500}, {0xc0047b4080?, 0xc0063ce000?}, {0x2?, 0x0?}, 0x0, 0x0)
	github.com/microsoft/typescript-go/internal/ls/findallreferences.go:602 +0x165
github.com/microsoft/typescript-go/internal/ls.handleCrossProject[...].func2.1()
	github.com/microsoft/typescript-go/internal/ls/crossproject.go:105 +0x231
github.com/microsoft/typescript-go/internal/core.(*parallelWorkGroup).Queue.func1()
	github.com/microsoft/typescript-go/internal/core/workgroup.go:40 +0x13
sync.(*WaitGroup).Go.func1()
	sync/waitgroup.go:239 +0x4a
created by sync.(*WaitGroup).Go in goroutine 1917
	sync/waitgroup.go:237 +0x73