Fix some more unconstrained types in msg_send results (#453)

The error I was investigating servo/servo#20474 (comment) turned out to be already be fixed by #428, but there was a few more cases of the same problem.

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 - Overhauled X11 window geometry calculations. `get_position` and `set_position` are more universally accurate across different window managers, and `get_outer_size` actually works now.
+- Fixed SIGSEGV/SIGILL crashes on macOS caused by stabilization of the `!` (never) type.
 
 # Version 0.12.0 (2018-04-06)
 

src/platform/macos/window.rs

@@ -470,13 +470,13 @@ impl Window2 {
                 }
                 if pl_attrs.titlebar_buttons_hidden {
                     let button = window.standardWindowButton_(NSWindowButton::NSWindowFullScreenButton);
-                    msg_send![button, setHidden:YES];
+                    let () = msg_send![button, setHidden:YES];
                     let button = window.standardWindowButton_(NSWindowButton::NSWindowMiniaturizeButton);
-                    msg_send![button, setHidden:YES];
+                    let () = msg_send![button, setHidden:YES];
                     let button = window.standardWindowButton_(NSWindowButton::NSWindowCloseButton);
-                    msg_send![button, setHidden:YES];
+                    let () = msg_send![button, setHidden:YES];
                     let button = window.standardWindowButton_(NSWindowButton::NSWindowZoomButton);
-                    msg_send![button, setHidden:YES];
+                    let () = msg_send![button, setHidden:YES];
                 }
                 if pl_attrs.movable_by_window_background {
                     window.setMovableByWindowBackground_(YES);