Fix size of fake screen

Unit tests (WML and C++ alike) require that the fake screen has nonzero
size. Thus, we again report a nonzero screen size with a fake screen.

Unfortunately, this didn't fix the unit test I was testing
(test_end_turn). The problem is that the null theme is returning that
the game area has zero size; however, I haven't found any differences
between 1.13 and master that would explain why the problem occurs in
master but not 1.13. I'll need to debug 1.13 separately later on...

src/tests/utils/fake_display.cpp

@@ -80,7 +80,7 @@ namespace test_utils {
 				fake_display_manager::get_manager()->get_display();
 
 		if(width >= 0 && height >= 0) {
-			display.video().make_test_fake();
+			display.video().make_test_fake(width, height);
 		}
 
 		return display;

src/video.cpp

@@ -51,6 +51,7 @@ CVideo::CVideo(FAKE_TYPES type)
 	, gl_context()
 #endif
 	, fake_screen_(false)
+	, fake_size_(0u, 0u)
 	, help_string_(0)
 	, updated_locked_(0)
 	, flip_locked_(0)
@@ -122,11 +123,14 @@ void CVideo::blit_surface(int x, int y, surface surf, SDL_Rect* srcrect, SDL_Rec
 void CVideo::make_fake()
 {
 	fake_screen_ = true;
+	fake_size_ = { 1024, 768 };
 }
 
-void CVideo::make_test_fake()
+void CVideo::make_test_fake(const unsigned width, const unsigned height)
 {
 	fake_interactive = true;
+	fake_size_.first = width;
+	fake_size_.second = height;
 }
 
 void CVideo::init_window()
@@ -205,7 +209,9 @@ void CVideo::set_window_mode(const MODE_EVENT mode, const point& size)
 SDL_Rect CVideo::screen_area(bool as_pixels) const
 {
 	if(!window) {
-		return sdl::empty_rect;
+		return {0, 0,
+			static_cast<int>(fake_size_.first),
+			static_cast<int>(fake_size_.second)};
 	}
 
 	// First, get the renderer size in pixels.

src/video.hpp

@@ -22,6 +22,7 @@
 #include <SDL_render.h>
 
 #include <memory>
+#include <utility>
 
 class surface;
 class texture;
@@ -55,8 +56,11 @@ public:
 
 	/**
 	 * Creates a fake frame buffer for the unit tests.
+	 *
+	 * @param width   The width of the buffer.
+	 * @param height  The height of the buffer
 	 */
-	void make_test_fake();
+	void make_test_fake(const unsigned width = 1024, const unsigned height = 768);
 
 	bool faked() const
 	{
@@ -258,6 +262,8 @@ private:
 	// if there is no display at all, but we 'fake' it for clients
 	bool fake_screen_;
 
+	std::pair<unsigned, unsigned> fake_size_;
+
 	/** Helper class to manage SDL events. */
 	class video_event_handler : public events::sdl_handler
 	{