app_server: don't reset brightness when switching workspaces

Fixes #16538.

src/servers/app/Desktop.cpp

@@ -514,6 +514,10 @@ Desktop::Init()
 	fVirtualScreen.SetConfiguration(*this,
 		fWorkspaces[0].CurrentScreenConfiguration());
 
+	float brightness = fWorkspaces[0].StoredScreenConfiguration().Brightness(0);
+	if (brightness > 0)
+		HWInterface()->SetBrightness(brightness);
+
 	if (fVirtualScreen.HWInterface() == NULL) {
 		debug_printf("Could not initialize graphics output. Exiting.\n");
 		return B_ERROR;

src/servers/app/ScreenConfigurations.cpp

@@ -153,6 +153,14 @@ ScreenConfigurations::SetBrightness(int32 id, float brightness)
 }
 
 
+float
+ScreenConfigurations::Brightness(int32 id)
+{
+	screen_configuration* configuration = fConfigurations.ItemAt(0);
+	return configuration->brightness;
+}
+
+
 void
 ScreenConfigurations::Remove(screen_configuration* configuration)
 {

src/servers/app/ScreenConfigurations.h

@@ -39,6 +39,7 @@ public:
 									const BRect& frame,
 									const display_mode& mode);
 			void				SetBrightness(int32 id, float brightness);
+			float				Brightness(int32 id);
 			void				Remove(screen_configuration* configuration);
 
 			status_t			Store(BMessage& settings) const;

src/servers/app/VirtualScreen.cpp

@@ -142,13 +142,6 @@ VirtualScreen::AddScreen(Screen* screen, ScreenConfigurations& configurations)
 	fFrame = screen->Frame();
 	item->frame = fFrame;
 
-	screen_configuration* config = configurations.CurrentByID(screen->ID());
-	if (config) {
-		float brightness = config->brightness;
-		if (brightness > 0)
-			fHWInterface->SetBrightness(brightness);
-	}
-
 	fScreenList.AddItem(item);
 
 	return B_OK;