Add FormBrowser.InvokeSafe and use it for CEF callbacks

Core/FormBrowser.cs

@@ -81,6 +81,15 @@ private void FormBrowser_WindowStateChanged(object sender, EventArgs e){
 
         // callback handlers
 
+        public void InvokeSafe(Action func){
+            if (InvokeRequired){
+                Invoke(func);
+            }
+            else{
+                func();
+            }
+        }
+
         public void OpenSettings(){
             // TODO
         }

Core/Handling/ContextMenuHandler.cs

@@ -1,4 +1,5 @@
 using CefSharp;
+using System;
 
 namespace TweetDick.Core.Handling{
     class ContextMenuHandler : IContextMenuHandler{
@@ -31,11 +32,17 @@ public void OnBeforeContextMenu(IWebBrowser browserControl, IBrowser browser, IF
         public bool OnContextMenuCommand(IWebBrowser browserControl, IBrowser browser, IFrame frame, IContextMenuParams parameters, CefMenuCommand commandId, CefEventFlags eventFlags){
             switch((int)commandId){
                 case MenuSettings:
-                    form.OpenSettings();
+                    form.InvokeSafe(() => {
+                        form.OpenSettings();
+                    });
+
                     return true;
 
                 case MenuAbout:
-                    form.OpenAbout();
+                    form.InvokeSafe(() => {
+                        form.OpenAbout();
+                    });
+
                     return true;
             }
 

Core/Handling/TweetDeckBridge.cs

@@ -7,7 +7,9 @@ public TweetDeckBridge(FormBrowser form){
         }
 
         public void OpenSettingsMenu(){
-            form.OpenSettings();
+            form.InvokeSafe(() => {
+                form.OpenSettings();
+            });
         }
 
         public void Log(string data){