external/zxing: Missing include (for std::nullptr_t)

Change-Id: I731eb3039f9f43ac05d3b60d5387ff44c5986a71
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/176049
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

external/zxing/UnpackedTarball_zxing.mk

@@ -15,6 +15,7 @@ $(eval $(call gb_UnpackedTarball_set_patchlevel,zxing,1))
 
 $(eval $(call gb_UnpackedTarball_add_patches,zxing, \
 	external/zxing/0001-add-ZXVersion-h.patch \
+	external/zxing/include.patch.0 \
 ))
 
 # vim: set noet sw=4 ts=4:

external/zxing/include.patch.0

@@ -0,0 +1,10 @@
+--- core/src/ZXNullable.h
++++ core/src/ZXNullable.h
+@@ -5,6 +5,7 @@
+ 
+ #pragma once
+ 
++#include <cstddef>
+ #include <stdexcept>
+ #include <utility>
+