Fix OffScreen's Address field

This fix ensures the Address field returns the correct value after
construction (instead of null).  The Address field setter is now private
as callers should use Load() to change url.

Author: jankurianski

CefSharp.OffScreen/ChromiumWebBrowser.cs

@@ -47,6 +47,7 @@ public ChromiumWebBrowser(string address, BrowserSettings browserSettings = null
             ResourceHandler = new DefaultResourceHandler();
 
             Cef.AddDisposable(this);
+            Address = address;
 
             managedCefBrowserAdapter = new ManagedCefBrowserAdapter(this, true);
             managedCefBrowserAdapter.CreateOffscreenBrowser(IntPtr.Zero, browserSettings ?? new BrowserSettings(), address);
@@ -197,7 +198,7 @@ public void AddWordToDictionary(string word)
             managedCefBrowserAdapter.AddWordToDictionary(word);
         }
 
-        public string Address { get; set; }
+        public string Address { get; private set; }
 
         public bool CanGoBack { get; private set; }