EXT-3313 Media Settings window has no background if viewer is too short

Code to set default floater position to top-left was causing incorrect
floater height computation when floater XML specified a bottom coordinate.
Reviewed with Callum.

indra/llui/llfloater.cpp

@@ -2703,6 +2703,18 @@ bool LLFloater::initFloaterXML(LLXMLNodePtr node, LLView *parent, LLXMLNodePtr o
 			output_node, output_params, &default_params);
 	}
 
+	// Default floater position to top-left corner of screen
+	// However, some legacy floaters have explicit top or bottom
+	// coordinates set, so respect their wishes.
+	if (!params.rect.top.isProvided() && !params.rect.bottom.isProvided())
+	{
+		params.rect.top.set(0);
+	}
+	if (!params.rect.left.isProvided() && !params.rect.right.isProvided())
+	{
+		params.rect.left.set(0);
+	}
+
 	setupParams(params, parent);
  	initFromParams(params);
 	

indra/newview/skins/default/xui/en/floater_media_settings.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8" standalone="yes" ?>
 <floater
  legacy_header_height="18"
- bottom="666" 
  can_close="true" 
  can_drag_on_left="false" 
  can_minimize="true"

indra/newview/skins/default/xui/en/widgets/floater.xml

@@ -9,8 +9,6 @@
  background_visible="true"
  background_opaque="false"
  header_height="25"
-         top="0"
-         left="0" 
  close_image="Icon_Close_Foreground"
  restore_image="Icon_Restore_Foreground"
  minimize_image="Icon_Minimize_Foreground"