cups: Add patch for bug where CUPS fails to save files to disk

Upstream report: apple/cups#5118

In addition to not saving files, this results in spam messages in the log once per second (Expiring subscriptions...)
which is what led me to discover this bug. The patch was made by hand because the patch from the commit does not apply.

pkgs/misc/cups/cups-clean-dirty.patch

@@ -0,0 +1,13 @@
+diff --git a/scheduler/main.c b/scheduler/main.c
+index 8925c8373..acf031684 100644
+--- a/scheduler/main.c
++++ b/scheduler/main.c
+@@ -893,7 +893,7 @@ main(int  argc,				/* I - Number of command-line args */
+     * Write dirty config/state files...
+     */
+
+-    if (DirtyCleanTime && current_time >= DirtyCleanTime && cupsArrayCount(Clients) == 0)
++    if (DirtyCleanTime && current_time >= DirtyCleanTime)
+       cupsdCleanDirty();
+
+ #ifdef __APPLE__

pkgs/misc/cups/default.nix

@@ -25,6 +25,7 @@ stdenv.mkDerivation rec {
       url = "https://git.archlinux.org/svntogit/packages.git/plain/trunk/cups-systemd-socket.patch?h=packages/cups";
       sha256 = "1ddgdlg9s0l2ph6l8lx1m1lx6k50gyxqi3qiwr44ppq1rxs80ny5";
     })
+    ./cups-clean-dirty.patch
   ];
 
   nativeBuildInputs = [ pkgconfig removeReferencesTo ];