'Intervals' are not calculated properly

[vitaliimelnychuk]

src/lcov.js responsible to build grouped array of lines that are not covered but it's broken once we have empty lines.

Would be great if we avoit this and have the full interval of uncovered lines without considering empty line as 'covered'

[vitaliimelnychuk]

It's happening with Node.js applications that are using jest or coverage to generate coverage lcov files.

[vitaliimelnychuk]

As an example, we can use this screenshot. All messages should be grouped into one instead as it doesn't make sense to consider empty space as not covered the line in this case.