fix crash: CoinControl "space" bug

Just like baf80c26a2

src/qt/coincontroltreewidget.cpp

@@ -17,6 +17,7 @@ void CoinControlTreeWidget::keyPressEvent(QKeyEvent *event)
     {
         event->ignore();
         int COLUMN_CHECKBOX = 0;
+        if(this->currentItem())
             this->currentItem()->setCheckState(COLUMN_CHECKBOX, ((this->currentItem()->checkState(COLUMN_CHECKBOX) == Qt::Checked) ? Qt::Unchecked : Qt::Checked));
     }
     else if (event->key() == Qt::Key_Escape) // press esc -> close dialog