getLineRanges reports contentLength of 1 for a file's first line if it's blank

[JoshuaKGoldberg]

See discussion in palantir/tslint#4518. If a file contains these lines:

let 1 = 2;

let b = 2;

...then the reported contentLengths are:

• 1
• 10
• 0
• 10

[ajafff]

@JoshuaKGoldberg I cannot reproduce this. I created #95 to add some tests for this.

I guess the line is not really empty but contains a BOM. I don't know if this function is the right place to handle this.