PixelPaint: Use correct thickness in `LineTool::on_second_paint()`

Previously, we were ignoring the scale of the editor in the second
paint step. If you were zoomed in, the size while you were drawing
was not the same as the size of the final shape.

Userland/Applications/PixelPaint/LineTool.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Mustafa Quraish <mustafa@cs.toronto.edu>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -100,7 +101,7 @@ void LineTool::on_second_paint(Layer const* layer, GUI::PaintEvent& event)
     painter.add_clip_rect(event.rect());
     auto preview_start = m_editor->layer_position_to_editor_position(*layer, m_line_start_position).to_type<int>();
     auto preview_end = m_editor->layer_position_to_editor_position(*layer, m_line_end_position).to_type<int>();
-    painter.draw_line(preview_start, preview_end, m_editor->color_for(m_drawing_button), m_thickness);
+    painter.draw_line(preview_start, preview_end, m_editor->color_for(m_drawing_button), m_thickness * m_editor->scale());
 }
 
 void LineTool::on_keydown(GUI::KeyEvent& event)