Qt: add initializer (CID 1159358).

Change-Id: I3002015d793e48c87017571f8997dd5a78438f75
Reviewed-on: https://code.wireshark.org/review/16272
Petri-Dish: Dario Lombardo <lomato@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>

ui/qt/sctp_graph_byte_dialog.cpp

@@ -38,6 +38,7 @@ SCTPGraphByteDialog::SCTPGraphByteDialog(QWidget *parent, sctp_assoc_info_t *ass
     ui(new Ui::SCTPGraphByteDialog),
     selected_assoc(assoc),
     cap_file_(cf),
+    frame_num(0),
     direction(dir)
 {
     ui->setupUi(this);