Merge pull request #5263 from miniak/mac-fix-maximize

Fix BrowserWindow.maximize/unmaximize on Mac

atom/browser/native_window_mac.mm

@@ -602,10 +602,16 @@ bool NativeWindowMac::IsVisible() {
 }
 
 void NativeWindowMac::Maximize() {
+  if (IsMaximized())
+    return;
+
   [window_ zoom:nil];
 }
 
 void NativeWindowMac::Unmaximize() {
+  if (!IsMaximized())
+    return;
+
   [window_ zoom:nil];
 }