Add support for empty lines inside jsdoc comment blocks

[AndrewOCC]

Adjusts normalisation logic so that empty lines in the middle of a comment aren't considered when calculating the indent.

Previously, the regex for SPACE_UNTIL_CONTENT would fail to include the '*' on an empty block comment line, as the * would meet the condition for the look-ahead (?=\S). This would give an inaccurate measure of the smallest indent.

For example, in this example:

     /**
       * comment
       * 
       * comment
       */

The matches on SPACE_UNTIL_CONTENT would be:
[" * "]
[" "]
[" * "]
The shortest indent value would be length 1, and the '*'s on each line wouldn't be stripped out, leading to the output:

* comment
* 
* comment

My current solution in this PR is to ignore empty lines when calculating the indent. Keen for feedback if there's a good way to adjust the SPACE_UNTIL_CONTENT regex to handle empty lines.

This was caught while debugging an issue in extract-react-types, where empty lines in JSDoc comments was breaking comment formatting.

[AndrewOCC]

Although this is technically a bug fix, I wonder if this should be a major release for the util, as this library has been stable for a long time and consumers may be making assumptions about how the library behaves in this edge case.

[AndrewOCC]

cc @Noviny, do you think this is a feasible fix for the library?