Anchor menu help text to the screen bottom to fix cropping of long text

Fix cropping of more than 4 line menu item help texts by anchoring
the bottom of the help text display to the bottom of the screen.
This prevents the help text from growing off of the screen when
the help text is long.

src/gui/menu.cpp

@@ -597,10 +597,12 @@ Menu::draw(DrawingContext& context)
     const int text_width = static_cast<int>(Resources::normal_font->get_text_width(m_items[m_active_item]->get_help()));
     const int text_height = static_cast<int>(Resources::normal_font->get_text_height(m_items[m_active_item]->get_help()));
 
+    const float margin_y = 16.0f;
+
     const Rectf text_rect(m_pos.x - static_cast<float>(text_width) / 2.0f - 8.0f,
-                          static_cast<float>(SCREEN_HEIGHT) - 48.0f - static_cast<float>(text_height) / 2.0f - 4.0f,
+                          static_cast<float>(SCREEN_HEIGHT) - margin_y - static_cast<float>(text_height) - 4.0f,
                           m_pos.x + static_cast<float>(text_width) / 2.0f + 8.0f,
-                          static_cast<float>(SCREEN_HEIGHT) - 48.0f + static_cast<float>(text_height) / 2.0f + 4.0f);
+                          static_cast<float>(SCREEN_HEIGHT) - margin_y + 4.0f);
 
     context.color().draw_filled_rect(Rectf(text_rect.p1() - Vector(4,4),
                                            text_rect.p2() + Vector(4,4)),
@@ -614,7 +616,7 @@ Menu::draw(DrawingContext& context)
                                      LAYER_GUI);
 
     context.color().draw_text(Resources::normal_font, m_items[m_active_item]->get_help(),
-                              Vector(m_pos.x, static_cast<float>(SCREEN_HEIGHT) - 48.0f - static_cast<float>(text_height) / 2.0f),
+                              Vector(m_pos.x, static_cast<float>(SCREEN_HEIGHT) - margin_y - static_cast<float>(text_height)),
                               ALIGN_CENTER, LAYER_GUI);
   }
 }