unicode-bom fixer insert BOM in appropriate location

[pantosha]

Tell us about your environment
Win 10, 64bit

• ESLint Version: v.3.15.0
• Node Version: v.7.5.0
• npm Version: v.4.1.2
  What parser (default, Babel-ESLint, etc.) are you using?
  default
  Please show your full configuration:

"unicode-bom" :  "error"

What did you do? Please include the actual source code causing the issue.
I called eslint --fix some.js.

// Some comments.
function someFunction() {
    // some code...
}

What did you expect to happen?

<U+FEFF>// Some comments.
function someFunction() {
    // some code...
}

What actually happened? Please include the actual, raw output from ESLint.

// Some comments.
<U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF><U+FEFF>function someFunction() {
    // some code...
}

[platinumazure]

@pantosha Looks like this is happening due to multipass autofix (and not detecting that the BOM was already inserted in a previous run). Thanks for reporting this!