Validate handles and catch COM errors when matching windows to code panes. Closes #2814

Author: comintern

Rubberduck.VBEEditor/Events/VBENativeServices.cs

@@ -170,12 +170,27 @@ private static void OnWindowFocusChange(object sender, WindowChangedEventArgs ev
 
         private static ICodePane GetCodePaneFromHwnd(IntPtr hwnd)
         {
-            var caption = hwnd.GetWindowText();
-            return _vbe.CodePanes.FirstOrDefault(x => x.Window.Caption.Equals(caption));
+            try
+            {
+                var caption = hwnd.GetWindowText();
+                return _vbe.CodePanes.FirstOrDefault(x => x.Window.Caption.Equals(caption));
+            }
+            catch
+            {
+                // This *should* only happen when a code pane window is removed and RD responds faster than
+                // the VBE removes it from the windows collection. TODO: Find a better method to match code panes
+                // to windows than testing the captions.
+                return null;
+            }
         }
 
         private static IWindow GetWindowFromHwnd(IntPtr hwnd)
         {
+            if (!User32.IsWindow(hwnd))
+            {
+                return null;
+            }
+
             var caption = hwnd.GetWindowText();
             return _vbe.Windows.FirstOrDefault(x => x.Caption.Equals(caption));
         }

Rubberduck.VBEEditor/WindowsApi/User32.cs

@@ -82,5 +82,14 @@ public static class User32
 
         [DllImport("user32.dll", CharSet = CharSet.Unicode)]
         internal static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string lclassName, string windowTitle);
+
+        /// <summary>
+        /// Validates a window handle.
+        /// </summary>
+        /// <param name="hWnd">The handle to validate.</param>
+        /// <returns></returns>
+        [DllImport("user32.dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        internal static extern bool IsWindow(IntPtr hWnd);
     }
 }