AlphaMask combines alphas instead of overwriting

git-svn-id: svn://svn.code.sf.net/p/magicseteditor/code/trunk@772 0fc631ac-6414-0410-93d0-97cfa31319b6

src/gfx/resample_image.cpp

@@ -126,6 +126,10 @@ void resample(const Image& img_in, Image& img_out) {
 }
 
 void resample_and_clip(const Image& img_in, Image& img_out, wxRect rect) {
+	// mask to alpha
+	if (img_in.HasMask() && !img_in.HasAlpha()) {
+		const_cast<Image&>(img_in).InitAlpha();
+	}
 	// starting position in data
 	int offset_in = (rect.x + img_in.GetWidth() * rect.y);
 	if (img_out.GetHeight() == rect.height) {