no-unbound-method warns on method existence check

[NN---]

Bug Report

• TSLint version: 5.5.0
• TypeScript version: 2.4.1
• Running TSLint via: gulp-tslint

TypeScript code being linted

var a = document.addEventListener ? document.addEventListener  : null;

Actual behavior

No error

Expected behavior

error noUnboundMethod: Avoid referencing unbound methods which may cause unintentional scoping of 'this'.

[adidahiya]

can you paste the verbose lint failure? which [line, col] is it failing on? it's more likely on the second instance of document.addEventListener, which is potentially a legit error (invoking a() is not the same as document.addEventListener()).

[NN---]

This is the code:

if (!document.documentElement.doScroll) {
}

TSLint:

[16:40:57] Using gulpfile C:\Projects\Agent-9.2\ChromeExtension\gulpfile.js
[16:40:57] Starting 'tslint'...
test.ts(30,6): error noUnboundMethod: Avoid referencing unbound methods which may cause unintentional scoping of 'this'.

[16:41:00] 'tslint' errored after 3.64 s
[16:41:00] Error in plugin 'gulp-tslint'
Message:
    Failed to lint: test.ts [30, 6]: Avoid referencing unbound methods which may cause unintentional scoping of 'this'..

[ajafff]

Fixed by #3349