neomutt: remove per-account empty lines

modules/programs/neomutt.nix

@@ -302,7 +302,8 @@ let
         "set signature = ${
           pkgs.writeText "signature.txt" account.signature.text
         }";
-    in ''
+    in concatStringsSep "\n" ([
+      ''
       # Generated by Home Manager.${
         optionalString cfg.unmailboxes ''
 
@@ -325,11 +326,10 @@ let
 
       # MTA section
       ${optionsStr (mtaSection account)}
-
-      ${optionalString (cfg.checkStatsInterval != null) mailCheckSection}
-
-      ${optionalString cfg.sidebar.enable sidebarSection}
-
+      '']
+      ++ (lib.optional (cfg.checkStatsInterval != null) mailCheckSection)
+      ++ (lib.optional cfg.sidebar.enable sidebarSection)
+      ++ [ ''
       # MRA section
       ${mraSection account}
 
@@ -337,9 +337,9 @@ let
       ${account.neomutt.extraConfig}
 
       ${signature}
-    ''
-    + optionalString (account.notmuch.enable && account.notmuch.neomutt.enable)
-    (notmuchSection account);
+    '' ]
+    ++ lib.optional (account.notmuch.enable && account.notmuch.neomutt.enable)
+    (notmuchSection account));
 
 in {
   options = {