[Fix] Fixed the drag&drop crash.

src/pdf_page_widget.cpp

@@ -6,6 +6,7 @@
 PDFPageWidget::PDFPageWidget(QWidget* parent) :
     QFrame(parent) {
 
+  selected = false;
   setAcceptDrops(true);
 
   /* Resize widget. */

src/pdf_page_widget.h

@@ -46,7 +46,7 @@ private:
   QPixmap         pixmap;
   QPushButton*    btn1, *btn2;
 
-  bool selected = false;
+  bool            selected;
 
 signals:
   void pageClicked(QMouseEvent* event, QString path);

src/pdf_table_widget.cpp

@@ -76,6 +76,8 @@ void PDFTableWidget::droppedPage(QString pathFrom, QString pathTo) {
    */
 
   /* Frontend operations here.. */
+  if(pathFrom == pathTo)
+    return;
   qDebug() << pathFrom;
   qDebug() << pathTo;
   PDFPageWidget* childFrom  = pageChilds[pathFrom];