psi-plus: bugfix for missing gstreamer dependencies

Voice messages don’t work without gstreamer “base” and “good” plugins.
This change adds a an override for GST_PLUGIN_SYSTEM_PATH_1_0
environment variable providing necessary dependencies.

pkgs/applications/networking/instant-messengers/psi-plus/default.nix

@@ -3,6 +3,10 @@
 , libidn, qca-qt5, libXScrnSaver, hunspell
 , libsecret, libgcrypt, libotr, html-tidy, libgpgerror, libsignal-protocol-c
 , usrsctp
+
+# Voice messages
+, voiceMessagesSupport ? true
+, gst_all_1
 }:
 
 mkDerivation rec {
@@ -27,8 +31,17 @@ mkDerivation rec {
     libidn qca-qt5 libXScrnSaver hunspell
     libsecret libgcrypt libotr html-tidy libgpgerror libsignal-protocol-c
     usrsctp
+  ] ++ lib.optionals voiceMessagesSupport [
+    gst_all_1.gst-plugins-base
+    gst_all_1.gst-plugins-good
   ];
 
+  preFixup = lib.optionalString voiceMessagesSupport ''
+    qtWrapperArgs+=(
+      --prefix GST_PLUGIN_SYSTEM_PATH_1_0 : "$GST_PLUGIN_SYSTEM_PATH_1_0"
+    )
+  '';
+
   meta = with lib; {
     homepage = "https://psi-plus.com";
     description = "XMPP (Jabber) client";