Bugfix: Scroll constraint favors top/left edge

For levels having a top/left scroll boundary, the top/left point takes
higher priority for resolving out-of-bounds scroll ranges instead of the
bottom/right.

This fixes a bug where you Zoom Out of a level far enough that the
entire boundaries of a Bounded level are smaller than the viewport into
the level. It could happen if playing normal levels in Play Mode on a
very high-resolution monitor. Previously, the level would anchor to the
bottom/right corner of your screen.

With the Zoom In/Out Feature this broke the ability to scroll well on
the level; so the easy fix is to put the X>0, Y>0 bounds check after the
above, so the level will hug the top/left corner of the screen which
fixes both problems.

pkg/uix/canvas_scrolling.go

@@ -67,18 +67,6 @@ func (w *Canvas) loopConstrainScroll() error {
 
 	var capped bool
 
-	// Constrain the top and left edges.
-	if w.wallpaper.pageType > level.Unbounded {
-		if w.Scroll.X > 0 {
-			w.Scroll.X = 0
-			capped = true
-		}
-		if w.Scroll.Y > 0 {
-			w.Scroll.Y = 0
-			capped = true
-		}
-	}
-
 	// Constrain the bottom and right for limited world sizes.
 	if w.wallpaper.pageType >= level.Bounded &&
 		w.wallpaper.maxWidth+w.wallpaper.maxHeight > 0 {
@@ -103,6 +91,18 @@ func (w *Canvas) loopConstrainScroll() error {
 		}
 	}
 
+	// Constrain the top and left edges.
+	if w.wallpaper.pageType > level.Unbounded {
+		if w.Scroll.X > 0 {
+			w.Scroll.X = 0
+			capped = true
+		}
+		if w.Scroll.Y > 0 {
+			w.Scroll.Y = 0
+			capped = true
+		}
+	}
+
 	if capped {
 		return errors.New("scroll limited by level constraint")
 	}