Fix indent_paragrahs/no final_gap line spacing bug

In case of no indent_paragraphs when formatted_text is called it
passes the text to render to Text.fill_formatted_text_box. Then the text
is rendered using the Box class and the Box class in combination with
the Wrap module takes care of spacing between lines. Spacing is present
regardless of final_gap value.

In case of indent_paragraphs set the situation is different.
formatted_text itself prints the first line separately and then the rest
of the text. As such, it has the responsibility to add spacing between
the first line and the rest on its own. When final_gap is set, as it is
by default, it works just fine. When final_gap is not set though, there
was no space between the first line and the second line of the text.

Since formatted_text calls draw_indented_formatted_line to render the
first line and draw_indented_formatted_line calls
fill_formatted_text_box with the single_line flag we can use the flag as
a secondary way to trigger adding a gap.

I also added a test case for a single line scenario because my initial
take on this issue introduced a different bug that caused a single-line
paragraph and another paragraph to have too much space between them.

lib/prawn/text.rb

@@ -382,7 +382,13 @@ def fill_formatted_text_box(text, options)
       @all_text_printed = box.everything_printed?
 
       self.y -= box.height
-      self.y -= box.line_gap + box.leading if @final_gap
+
+      # If there's no remaining_text we don't really want to treat this line
+      # in a special way, we printed everything we wanted so the special
+      # single_line logic should not be triggered here.
+      if @final_gap || (options[:single_line] && !@all_text_printed)
+        self.y -= box.line_gap + box.leading
+      end
 
       remaining_text
     end

spec/prawn/text_spec.rb

@@ -491,6 +491,44 @@
         end
       end
 
+      describe 'when :final_gap is set to false, there should still be ' \
+        'a gap between the first line and the rest' do
+        it 'spaces the first and the second line correctly' do
+          text = 'hello ' * 30
+          original_y = pdf.y
+          # First rendering with no indentation so we know what the correct
+          # render height should be
+          pdf.text(text, final_gap: false)
+          height_with_no_indentation = original_y - pdf.y
+          y_between_paragraphs = pdf.y
+          # The indentation size doesn't matter, it's about triggering
+          # a different path in the code
+          pdf.text(text, indent_paragraphs: 1, final_gap: false)
+          height_with_indentation = y_between_paragraphs - pdf.y
+          expect(height_with_indentation).to be_within(0.0001)
+            .of(height_with_no_indentation)
+        end
+      end
+
+      describe 'single line height with no final_gap should not depend on '\
+        'indentation' do
+        it 'does not affect the height of a single line' do
+          text = 'hello'
+          original_y = pdf.y
+          # First rendering with no indentation so we know what the correct
+          # render height should be
+          pdf.text(text, final_gap: false)
+          height_with_no_indentation = original_y - pdf.y
+          y_between_paragraphs = pdf.y
+          # The indentation size doesn't matter, it's about triggering
+          # a different path in the code
+          pdf.text(text, indent_paragraphs: 1, final_gap: false)
+          height_with_indentation = y_between_paragraphs - pdf.y
+          expect(height_with_indentation).to be_within(0.0001)
+            .of(height_with_no_indentation)
+        end
+      end
+
       describe 'when wrap to new page, and first line of new page' \
               ' is not the start of a new paragraph, that line should' \
               ' not be indented' do