Assert in inferFromUsages when typing function with rest args

[RyanCavanaugh]

Code:

function f(...

Trace:

Exception on executing command {"seq":403,"type":"request","command":"getCodeFixes","arguments":{"file":"c:/Throwaway/a.ts","startLine":1,"startOffset":12,"endLine":1,"endOffset":15,"errorCodes":[7019,1003]}}:

    Debug Failure. False expression: Found no references!

    Error: Debug Failure. False expression: Found no references!
    at getReferences (C:\github\TypeScript\built\local\tsserver.js:92872:26)
    at inferTypeForVariableFromUsage (C:\github\TypeScript\built\local\tsserver.js:92877:67)
    at C:\github\TypeScript\built\local\tsserver.js:92812:108
    at Object.map (C:\github\TypeScript\built\local\tsserver.js:1710:29)
    at getCodeActionForParameters (C:\github\TypeScript\built\local\tsserver.js:92812:24)
    at Object.getActionsForAddExplicitTypeAnnotation [as getCodeActions] (C:\github\TypeScript\built\local\tsserver.js:92771:28)
    at C:\github\TypeScript\built\local\tsserver.js:90978:33
    at Object.forEach (C:\github\TypeScript\built\local\tsserver.js:1511:30)
    at Object.getFixes (C:\github\TypeScript\built\local\tsserver.js:90977:16)
    at C:\github\TypeScript\built\local\tsserver.js:96798:35
    at Object.flatMap (C:\github\TypeScript\built\local\tsserver.js:1771:25)
    at Object.getCodeFixesAtPosition (C:\github\TypeScript\built\local\tsserver.js:96796:23)
    at IOSession.Session.getCodeFixes (C:\github\TypeScript\built\local\tsserver.js:104325:64)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (C:\github\TypeScript\built\local\tsserver.js:103203:61)
    at C:\github\TypeScript\built\local\tsserver.js:104488:88
    at IOSession.Session.executeWithRequestId (C:\github\TypeScript\built\local\tsserver.js:104479:28)
    at IOSession.Session.executeCommand (C:\github\TypeScript\built\local\tsserver.js:104488:33)
    at IOSession.Session.onMessage (C:\github\TypeScript\built\local\tsserver.js:104508:35)
    at Interface.<anonymous> (C:\github\TypeScript\built\local\tsserver.js:105760:27)
    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)