texture: Strip alpha channel when premultiplying

Author: cohaereo

src/texture/mod.rs

@@ -726,6 +726,7 @@ impl Texture {
                 c[0] = (c[0] as f32 * c[3] as f32 / 255.) as u8;
                 c[1] = (c[1] as f32 * c[3] as f32 / 255.) as u8;
                 c[2] = (c[2] as f32 * c[3] as f32 / 255.) as u8;
+                c[3] = 255;
             }
         }