Fix bugs on initial create and null exception.

For the null exception, it's when the last tab gets closed and the
code tries to focus on ActiveDocument. Since it no longer exists, a
null pointer exception is thrown.

The second bug is on the creation of the first tab. It needs to be
focused after it is created.

SuperPutty/frmSuperPutty.cs

@@ -277,9 +277,16 @@ public bool IsActiveDocument(ctlPuttyPanel panel)
         /// <param name="e"></param>
         private void dockPanel1_ActiveDocumentChanged(object sender, EventArgs e)
         {
-            FocusCurrentTab();
-            dockPanel1.ActiveDocument.TabTextColor = null;
-            dockPanel1.ActiveDocument.DockHandler.RefreshPaneChanges();
+            if (dockPanel1.ActiveDocument != null)
+            {
+                FocusCurrentTab();
+                dockPanel1.ActiveDocument.TabTextColor = null;
+                dockPanel1.ActiveDocument.DockHandler.RefreshPaneChanges();
+            }
+            else
+            {
+                this.Focus();
+            }
         }
 
         private void frmSuperPutty_Activated(object sender, EventArgs e)
@@ -447,7 +454,7 @@ public void CreatePuttyPanel(SessionData sessionData, bool isPutty)
                         this.BeginInvoke((MethodInvoker)delegate()
                         {
                             sessionPanel.Close();
-                         });
+                        });
                     }
                     else
                     {
@@ -458,6 +465,7 @@ public void CreatePuttyPanel(SessionData sessionData, bool isPutty)
 
             sessionPanel = new ctlPuttyPanel(this, sessionData, callback, isPutty);
             sessionPanel.Show(dockPanel1, sessionData.LastDockstate);
+            FocusCurrentTab();
         }
 
         private void newMintty_Click(object sender, EventArgs e)