Make empty inherit's more consistent and convenient

This might happen if you temporarily remove all inherits, in which case
the formatter shouldn't remove the spacing that was there.

E.g. I might have this initially

    inherit a b;

    inherit
      c
      d
      ;

removing all the bindings gives me

    inherit ; # I already have the space that I'll need

    inherit # I can just press enter here to add one
      ;

which shouldn't be changed, because it's easier like this to insert new
entries again, compared to

    inherit;

This also makes it more consistent with the parent commit's change

src/Nixfmt/Pretty.hs

@@ -127,10 +127,8 @@ instance Pretty Binder where
   pretty (Inherit inherit Nothing ids semicolon) =
     group $
       pretty inherit
-        <> ( if null ids
-              then pretty semicolon
-              else sep <> nest (sepBy sep ids <> nosep <> pretty semicolon)
-           )
+        <> sep
+        <> nest (sepBy sep ids <> nosep <> pretty semicolon)
     where
       -- Only allow a single line if it's already on a single line and has few enough elements
       (sep, nosep) = if sourceLine inherit == sourceLine semicolon && length ids < 4 then (line, line') else (hardline, hardline)

test/diff/inherit/out.nix

@@ -1,7 +1,7 @@
 [
   {
     # empty inherit o.O
-    inherit;
+    inherit ;
     inherit aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;
   }
   {
@@ -83,7 +83,8 @@
   }
 
   {
-    inherit;
+    inherit
+      ;
     inherit
       a
       ;