mesa: Free memory allocated for luminance in readpixels.

Cc: "10.4, 10.5" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
diff --git a/src/mesa/main/readpix.c b/src/mesa/main/readpix.c
index 2e4a460..ed0104c 100644
--- a/src/mesa/main/readpix.c
+++ b/src/mesa/main/readpix.c
@@ -594,6 +594,7 @@
       _mesa_format_convert(dst, dst_format, dst_stride,
                            luminance, luminance_format, luminance_stride,
                            width, height, NULL);
+      free(luminance);
    } else {
       _mesa_pack_luminance_from_rgba_integer(width * height, src, !src_is_uint,
                                              dst, format, type);