[Qt Expert Info dialogue] remove our tap listener when the dialogue is destroyed

if we don't do this, there'll be a dangling tap listener and we'll see a
crash when its reset method is called

this can be triggered by opening another expert info dialogue, this will
invoke cf_retap_packets() and reset_tap_listeners() which in turn calls
the reset method of each registered tap listener

Bug: 11432
Change-Id: I8fc13351666c875e1a3641f31bada8e80d167ab2
Reviewed-on: https://code.wireshark.org/review/9979
Petri-Dish: Martin Kaiser <wireshark@kaiser.cx>
Reviewed-by: Gerald Combs <gerald@wireshark.org>

ui/qt/expert_info_dialog.cpp

@@ -205,6 +205,7 @@ ExpertInfoDialog::ExpertInfoDialog(QWidget &parent, CaptureFile &capture_file) :
 
 ExpertInfoDialog::~ExpertInfoDialog()
 {
+    remove_tap_listener(this);
     delete ui;
 }