QT: Fix QString -> char* memory leak in Hist window.

xtt/lib/xtt/qt/xtt_hist_qt.cqt

@@ -375,15 +375,24 @@ void HistQtWidget::ok_btn()
   hist->eventPrio_D = hist->prioD_toggle_w->isChecked();
 
   hist->minTime_str = (char*)malloc(hist->start_time_entry_w->text().length() + 1);
-  strcpy(hist->minTime_str, qPrintableLatin1(hist->start_time_entry_w->text()));
   hist->maxTime_str = (char*)malloc(hist->stop_time_entry_w->text().length() + 1);
-  strcpy(hist->maxTime_str, qPrintableLatin1(hist->stop_time_entry_w->text()));
   hist->eventText_str = (char*)malloc(hist->event_text_entry_w->text().length() + 1);
-  strcpy(hist->eventText_str, qPrintableLatin1(hist->event_text_entry_w->text()));
   hist->eventName_str = (char*)malloc(hist->event_name_entry_w->text().length() + 1);
+  strcpy(hist->minTime_str, qPrintableLatin1(hist->start_time_entry_w->text()));
+  strcpy(hist->maxTime_str, qPrintableLatin1(hist->stop_time_entry_w->text()));
+  strcpy(hist->eventText_str, qPrintableLatin1(hist->event_text_entry_w->text()));
   strcpy(hist->eventName_str, qPrintableLatin1(hist->event_name_entry_w->text()));
 
   hist->get_hist_list();
+
+  free(hist->minTime_str);
+  free(hist->maxTime_str);
+  free(hist->eventText_str);
+  free(hist->eventName_str);
+  hist->minTime_str = NULL;
+  hist->maxTime_str = NULL;
+  hist->eventText_str = NULL;
+  hist->eventName_str = NULL;
 }
 
 void HistQtWidget::activate_print()