[Qt] make most Windows appear centered on main GUI

- remove default value for parent variable in dialogs, which should appear
  centered over main GUI and pass appropriate value
- add some addition NULL pointer checks

1 files changed, 1 insertions, 1 deletions

diff --git a/src/qt/signverifymessagedialog.h b/src/qt/signverifymessagedialog.h
index c741450b8a..bba861649a 100644
--- a/src/qt/signverifymessagedialog.h
+++ b/src/qt/signverifymessagedialog.h
@@ -18,7 +18,7 @@ class SignVerifyMessageDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit SignVerifyMessageDialog(QWidget *parent = 0);
+    explicit SignVerifyMessageDialog(QWidget *parent);
     ~SignVerifyMessageDialog();
 
     void setModel(WalletModel *model);