Move png_set_swap later in PNG write or it is ignored (fixes 16bpc PNGs)

apps/shared/avifpng.c

diff --git a/apps/shared/avifpng.c b/apps/shared/avifpng.c
index 87dab49..933d0e4 100644
--- a/apps/shared/avifpng.c
+++ b/apps/shared/avifpng.c
@@ -177,10 +177,6 @@
         }
     }
 
-    if (rgbDepth > 8) {
-        png_set_swap(png);
-    }
-
     png_set_IHDR(
         png, info, avif->width, avif->height, rgbDepth, PNG_COLOR_TYPE_RGBA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
     if (avif->profileFormat == AVIF_PROFILE_FORMAT_ICC) {
@@ -197,6 +193,10 @@
         rowPointers[y] = &rgb.pixels[y * rgb.rowBytes];
     }
 
+    if (rgbDepth > 8) {
+        png_set_swap(png);
+    }
+
     png_write_image(png, rowPointers);
     png_write_end(png, NULL);