Null deref fixes / cleanups

src/plane.cpp

@@ -105,10 +105,12 @@ void Plane::setBitmap(Bitmap *value)
 {
 	GUARD_DISPOSED;
 
-	if (value)
-		value->ensureNonMega();
-
 	p->bitmap = value;
+
+	if (!value)
+		return;
+
+	value->ensureNonMega();
 }
 
 void Plane::setOX(int value)

src/sprite.cpp

@@ -152,10 +152,13 @@ void Sprite::setBitmap(Bitmap *bitmap)
 	if (p->bitmap == bitmap)
 		return;
 
-	if (bitmap)
+	p->bitmap = bitmap;
+
+	if (!bitmap)
+		return;
+
 	bitmap->ensureNonMega();
 
-	p->bitmap = bitmap;
 	*p->srcRect = bitmap->rect();
 	p->onSrcRectChange();
 	p->quad.setPosRect(p->srcRect->toFloatRect());

src/window.cpp

@@ -717,23 +717,28 @@ void Window::setWindowskin(Bitmap *value)
 {
 	GUARD_DISPOSED;
 
-	if (value)
-		value->ensureNonMega();
-
 	p->windowskin = value;
+
+	if (!value)
+		return;
+
+	value->ensureNonMega();
 }
 
 void Window::setContents(Bitmap *value)
 {
 	GUARD_DISPOSED;
 
-	if (value)
-		value->ensureNonMega();
+	if (p->contents == value)
+		return;
 
 	p->contents = value;
 	p->controlsVertDirty = true;
 
-	if (value)
+	if (!value)
+		return;
+
+	value->ensureNonMega();
 	p->contentsQuad.setTexPosRect(value->rect(), value->rect());
 }