Cocoa: Fix missing check for selector

Fixes #1457.

src/cocoa_window.m

@@ -857,7 +857,9 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
     [window->ns.object setDelegate:window->ns.delegate];
     [window->ns.object setAcceptsMouseMovedEvents:YES];
     [window->ns.object setRestorable:NO];
+
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
+    if ([window->ns.object respondsToSelector:@selector(setTabbingMode:)])
         [window->ns.object setTabbingMode:NSWindowTabbingModeDisallowed];
 #endif