v fmt: fix extra space for anon struct (#16131)

doc/docs.md

@@ -2133,7 +2133,7 @@ with a struct name.
 
 ```v
 struct Book {
-	author struct  {
+	author struct {
 		name string
 		age  int
 	}

examples/gg/arcs_and_slices.v

@@ -19,7 +19,7 @@ enum Selection {
 struct App {
 mut:
 	gg    &gg.Context = unsafe { nil }
-	mouse struct  {
+	mouse struct {
 	mut:
 		x f32
 		y f32

vlib/v/checker/tests/anon_structs_visibility/amod/amod.v

@@ -2,7 +2,7 @@ module amod
 
 pub struct Foo {
 pub mut:
-	bar struct  {
+	bar struct {
 	pub mut:
 		baz int
 	}

vlib/v/fmt/struct.v

@@ -12,13 +12,14 @@ pub fn (mut f Fmt) struct_decl(node ast.StructDecl, is_anon bool) {
 		f.write('pub ')
 	}
 	if node.is_union {
-		f.write('union ')
+		f.write('union')
 	} else {
-		f.write('struct ')
+		f.write('struct')
 	}
-	f.write_language_prefix(node.language)
 	name := node.name.after('.') // strip prepended module
 	if !is_anon {
+		f.write(' ')
+		f.write_language_prefix(node.language)
 		f.write(name)
 	}
 	f.write_generic_types(node.generic_types)

vlib/v/tests/struct_test.v

@@ -416,7 +416,7 @@ fn test_struct_update() {
 // Test anon structs
 struct Book {
 	x      Foo
-	author struct  {
+	author struct {
 		name string
 		age  int
 	}