wslu: supply default conf

This fixes running `wslvar USERNAME` after one of the recent update.

pkgs/tools/system/wslu/default.nix

@@ -14,6 +14,15 @@ stdenv.mkDerivation rec {
     hash = "sha256-yhugh836BoSISbTu19ubLOrz5X31Opu5QtCR0DXrbWc=";
   };
 
+  patches = [
+    ./fallback-conf-nix-store.diff
+  ];
+
+  postPatch = ''
+    substituteInPlace src/wslu-header \
+      --subst-var out
+  '';
+
   makeFlags = [
     "DESTDIR=$(out)"
     "PREFIX="

pkgs/tools/system/wslu/fallback-conf-nix-store.diff

@@ -0,0 +1,22 @@
+diff --git a/src/wslu-header b/src/wslu-header
+index 5f33925..159c6af 100644
+--- a/src/wslu-header
++++ b/src/wslu-header
+@@ -169,11 +169,17 @@ if [ -f "$HOME/.config/wslu/conf" ]; then
+ 	debug_echo "$HOME/.config/wslu/conf found, sourcing"
+ 	source "$HOME/.config/wslu/conf"
+ fi
++
+ if [ -f "$HOME/.wslurc" ]; then
+ 	debug_echo "$HOME/.wslurc found, sourcing"
+ 	source "$HOME/.wslurc"
+ fi
+ 
++if [ -f "@out@/share/wslu/conf" ]; then
++	debug_echo "@out@/share/wslu/conf found, sourcing"
++	source "@out@/share/wslu/conf"
++fi
++
+ # functions
+ 
+ function help {