Fix https://github.com/Microsoft/TypeScript/issues/15436

[ochanje210]

I have found out that getTypeOfSymbol does not check if its parameter, symbol, exists and produce TypeError: Cannot read property 'flags' of undefined when using no-unused-variable from TSLint.

Fixes palantir/tslint#3001
Also, it is related to #15436

[msftclas]

@ochanje210,
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[DanielRosenwasser]

Hey @ochanje210, thanks for the PR. I don't necessarily know if this is the correct fix - do other similar functions check for if a symbol is defined? Or do all callers need to make sure that symbols are defined before calling getTypeOfSymbol?

Additionally, we need a failing test case to ensure we don't have regressions.

[faceach]

This change is necessary, and many ts-lint mistakes are hidden because of this issue.

[ochanje210]

Thank you for your comments and apologies for being late since I've been busy lately. :(
I will try to find out if this is necessarily correct fix, in addition to the failing test case very soon. Also, anyone is welcome to continue this before I could do so.

[msftclas]

@ochanje210,
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Thanks,
Microsoft Pull Request Bot

[ochanje210]

Closing this since it seems fixed with this commit: palantir/tslint@a479f43