tor-browser-bundle-bin: fix unbound variables

pkgs/applications/networking/browsers/tor-browser-bundle-bin/default.nix

@@ -357,7 +357,7 @@ stdenv.mkDerivation rec {
       TMPDIR="\''${TMPDIR:-/tmp}" \
       HOME="\$HOME" \
       XAUTHORITY="\''${XAUTHORITY:-\$HOME/.Xauthority}" \
-      DISPLAY="\$DISPLAY" \
+      DISPLAY="\''${DISPLAY:-}" \
       DBUS_SESSION_BUS_ADDRESS="\''${DBUS_SESSION_BUS_ADDRESS:-unix:path=\$XDG_RUNTIME_DIR/bus}" \\
       \
       XDG_DATA_HOME="\$HOME/.local/share" \
@@ -366,10 +366,10 @@ stdenv.mkDerivation rec {
       PULSE_SERVER="\''${PULSE_SERVER:-}" \
       PULSE_COOKIE="\''${PULSE_COOKIE:-}" \
       \
-      MOZ_ENABLE_WAYLAND=\$MOZ_ENABLE_WAYLAND \
-      WAYLAND_DISPLAY="\$WAYLAND_DISPLAY" \
-      XDG_RUNTIME_DIR="\$XDG_RUNTIME_DIR" \
-      XCURSOR_PATH="\$XCURSOR_PATH" \
+      MOZ_ENABLE_WAYLAND="\''${MOZ_ENABLE_WAYLAND:-}" \
+      WAYLAND_DISPLAY="\''${WAYLAND_DISPLAY:-}" \
+      XDG_RUNTIME_DIR="\''${XDG_RUNTIME_DIR:-}" \
+      XCURSOR_PATH="\''${XCURSOR_PATH:-}" \
       \
       APULSE_PLAYBACK_DEVICE="\''${APULSE_PLAYBACK_DEVICE:-plug:dmix}" \
       \
@@ -409,9 +409,7 @@ stdenv.mkDerivation rec {
     LD_LIBRARY_PATH=$libPath $TBB_IN_STORE/TorBrowser/Tor/tor --version >/dev/null
 
     echo "Checking tor-browser wrapper ..."
-    DISPLAY="" MOZ_ENABLE_WAYLAND="" WAYLAND_DISPLAY="" XAUTHORITY="" \
-      XCURSOR_PATH="" XDG_RUNTIME_DIR="" XDG_SESSION_TYPE="" \
-      DBUS_SESSION_BUS_ADDRESS="" TBB_HOME=$(mktemp -d) \
+      TBB_HOME=$(mktemp -d) \
       $out/bin/tor-browser --version >/dev/null
   '';