Fix SD-1793 - ObjectDisposedException in System.Windows.Forms.Integration.WinFormsAdapter

src/AddIns/DisplayBindings/FormsDesigner/Project/Src/DesignerViewContent.cs

@@ -494,8 +494,13 @@ namespace ICSharpCode.FormsDesigner
 						host.Dispose();
 					return;
 				}
-				if (host != null && host.Child == value)
-					return;
+				if (host != null) {
+					if (host.IsDisposed) {
+						host = null;
+					} else if (host.Child == value) {
+						return;
+					}
+				}
 				if (host == null) {
 					host = new SDWindowsFormsHost(true);
 					host.ServiceObject = this;

src/Main/Base/Project/Src/Util/SDWindowsFormsHost.cs

@@ -207,12 +207,15 @@ namespace ICSharpCode.SharpDevelop.Gui
 		/// </remarks>
 		public bool DisposeChild { get; set; }
 		
+		public bool IsDisposed { get; private set; }
+		
 		protected override void Dispose(bool disposing)
 		{
 			if (disposing && !this.DisposeChild && Child != null) {
 				// prevent child from being disposed
 				Child = null;
 			}
+			IsDisposed = disposing;
 			base.Dispose(disposing);
 		}
 	}