TypeError: Cannot read property 'charCount' of undefined in 'LineNode.charOffsetToLineInfo' during 'navtree'

[aozgaa]

This issue comes from crash dumps in telemetry. We've tried to de-duplicate issues on a best-effort basis, comparing the sequence of methods called and the command requested while ignoring line numbers.
TypeScript Version Prefix: 2.7.1
VSCode Version 1.19.2
command requested: navtree
hitting sessions: 406
proportion of all sessions: 0.0015156436072317851
five line hash: 78f8cedc7b3dcde1d4b897f52edf69f8
stack

TypeError: Cannot read property 'charCount' of undefined
    at LineNode.charOffsetToLineInfo (tsserver.js:91053:79)
    at LineIndex.positionToLineOffset (tsserver.js:90802:36)
    at ScriptVersionCache.positionToLineOffset (tsserver.js:90725:50)
    at TextStorage.positionToLineOffset (tsserver.js:84664:33)
    at ScriptInfo.positionToLineOffset (tsserver.js:84901:41)
    at IOSession.Session.toLocationTextSpan (tsserver.js:90084:39)
    at unknown (tsserver.js:90078:74)
    at Array.map (native)
    at IOSession.Session.toLocationNavigationTree (tsserver.js:90078:39)
    at IOSession.Session.getNavigationTree (tsserver.js:90094:32)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (tsserver.js:89106:61)
    at unknown (tsserver.js:90393:88)
    at IOSession.Session.executeWithRequestId (tsserver.js:90384:28)
    at IOSession.Session.executeCommand (tsserver.js:90393:33)
    at IOSession.Session.onMessage (tsserver.js:90413:35)
    at Interface.<anonymous> (tsserver.js:91614:27)
    at emitOne (events.js:96:13)
    at Interface.emit (events.js:191:7)
    at Interface._onLine (readline.js:241:10)
    at Interface._normalWrite (readline.js:384:12)
    at Socket.ondata (readline.js:101:10)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:191:7)
    at readableAddChunk (_stream_readable.js:178:18)
    at Socket.Readable.push (_stream_readable.js:136:10)
    at Pipe.onread (net.js:560:20)

[aozgaa]

This issue reproduced in the following context:
TypeScript Version Prefix: 2.7.2
VSCode Version 1.21.0-insider
command requested: navtree
hitting sessions: 168
proportion of all sessions: 0.003449054589500914
stack

TypeError: Cannot read property 'charCount' of undefined
    at LineNode.charOffsetToLineInfo (tsserver.js:91213:79)
    at LineIndex.positionToLineOffset (tsserver.js:90962:36)
    at ScriptVersionCache.positionToLineOffset (tsserver.js:90885:50)
    at TextStorage.positionToLineOffset (tsserver.js:84824:33)
    at ScriptInfo.positionToLineOffset (tsserver.js:85061:41)
    at IOSession.Session.toLocationTextSpan (tsserver.js:90244:39)
    at unknown (tsserver.js:90238:74)
    at Array.map (native)
    at IOSession.Session.toLocationNavigationTree (tsserver.js:90238:39)
    at IOSession.Session.getNavigationTree (tsserver.js:90254:32)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (tsserver.js:89266:61)
    at unknown (tsserver.js:90553:88)
    at IOSession.Session.executeWithRequestId (tsserver.js:90544:28)
    at IOSession.Session.executeCommand (tsserver.js:90553:33)
    at IOSession.Session.onMessage (tsserver.js:90573:35)
    at Interface.<anonymous> (tsserver.js:91774:27)
    at emitOne (events.js:96:13)
    at Interface.emit (events.js:191:7)
    at Interface._onLine (readline.js:241:10)
    at Interface._normalWrite (readline.js:384:12)
    at Socket.ondata (readline.js:101:10)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:191:7)
    at readableAddChunk (_stream_readable.js:178:18)
    at Socket.Readable.push (_stream_readable.js:136:10)
    at Pipe.onread (net.js:560:20)