navidrome: fix wrapper arguments escaping

pkgs/servers/misc/navidrome/default.nix

···
     runHook postInstall
   '';
 
-  postFixup = ''
+  postFixup = optionalString ffmpegSupport ''
     wrapProgram $out/bin/navidrome \
-      --prefix PATH : ${makeBinPath (optional ffmpegSupport ffmpeg)}
+      --prefix PATH : ${makeBinPath [ ffmpeg ]}
   '';
 
   passthru.tests.navidrome = nixosTests.navidrome;