Fix spacing of pretty printed const item without body

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1116,9 +1116,9 @@ impl<'a> State<'a> {
         self.print_ident(ident);
         self.word_space(":");
         self.print_type(ty);
-        self.space();
         self.end(); // end the head-ibox
         if let Some(body) = body {
+            self.space();
             self.word_space("=");
             self.print_expr(body);
         }