Fix function call and variable screw up

lib.rs

@@ -134,8 +134,8 @@ pub fn load_png_from_memory(image: &[u8]) -> Result<Image,~str> {
         ffi::png_set_interlace_handling(png_ptr);
         ffi::png_read_update_info(png_ptr, info_ptr);
 
-        let updated_color_type = ffi::png_get_bit_depth(&*png_ptr, &*info_ptr);
-        let updated_bit_depth = ffi::png_get_color_type(&*png_ptr, &*info_ptr);
+        let updated_bit_depth = ffi::png_get_bit_depth(&*png_ptr, &*info_ptr);
+        let updated_color_type = ffi::png_get_color_type(&*png_ptr, &*info_ptr);
 
         let (color_type, pixel_width) = match (updated_color_type as c_int, updated_bit_depth) {
             (ffi::COLOR_TYPE_RGB, 8) |