Formatted text has wrong leading with one line paragraphs

[maerch]

What's wrong: If you are indenting a paragraph, but have only one line to print, it will be printed by draw_indented_formatted_line completely. Thus, remaining_text is empty, but Prawn tries to print it anyway. The problem is that fill_formatted_text_box is still changing the y value of the document if you specify leading:

      self.y -= box.height
      self.y -= box.line_gap + box.leading if @final_gap

box.height and box.line_gap are zero for an empty remaining text, but box.leading is not. This causes a wrong leading in your text if you have single line paragraphs.

Example:

require "prawn"

Prawn::Document.generate("too_much_leading.pdf") do
  text_options = {
    indent_paragraphs: 30,
    leading: 20
  }
  text "Hello World!", text_options
  text "Second paragraph on more than one line!"*5, text_options
  text "Third paragraph on more than one line!"*5, text_options
end

Space between the first paragraphs is too large. It should have the same leading as between the second and third paragraph.

[pointlessone]

@maerch Thank you for your contribution. I've rebased this PR on master and merged it but GitHub didn't pick it up. I will close this PR now.