messageviewerplugins: don't create widget just to hide it

Called by ViewerPluginToolManager::closeAllTools() in
ViewerPrivate::resetStateForNewMessage().

plugins/messageviewerplugins/createeventplugin/viewerplugincreateeventinterface.cpp

@@ -64,7 +64,9 @@ void ViewerPluginCreateEventInterface::setMessage(const KMime::Message::Ptr &val
 
 void ViewerPluginCreateEventInterface::closePlugin()
 {
-    widget()->slotCloseWidget();
+    if (mEventEdit) {
+        mEventEdit->slotCloseWidget();
+    }
 }
 
 void ViewerPluginCreateEventInterface::showWidget()

plugins/messageviewerplugins/createnoteplugin/viewerplugincreatenoteinterface.cpp

@@ -62,7 +62,9 @@ void ViewerPluginCreatenoteInterface::setMessage(const KMime::Message::Ptr &valu
 
 void ViewerPluginCreatenoteInterface::closePlugin()
 {
-    widget()->slotCloseWidget();
+    if (mNoteEdit) {
+        mNoteEdit->slotCloseWidget();
+    }
 }
 
 Akonadi::Relation ViewerPluginCreatenoteInterface::relatedNoteRelation() const

plugins/messageviewerplugins/createtodoplugin/viewerplugincreatetodointerface.cpp

@@ -59,7 +59,9 @@ void ViewerPluginCreateTodoInterface::setMessage(const KMime::Message::Ptr &valu
 
 void ViewerPluginCreateTodoInterface::closePlugin()
 {
-    widget()->slotCloseWidget();
+    if (mTodoEdit) {
+        mTodoEdit->slotCloseWidget();
+    }
 }
 
 void ViewerPluginCreateTodoInterface::showWidget()