qt: Prevent non-functional GUI from popping up during Init

When a InitError or InitWarning happens, the
GUI pops up but is unusable (until Init finishes).

This is caused by showNormalIfMinimized. Add a message
flag to skip this call for Init errors or warnings.

src/qt/bitcoingui.cpp

@@ -681,8 +681,11 @@ void BitcoinGUI::message(const QString &title, const QString &message, unsigned
         if (!(buttons = (QMessageBox::StandardButton)(style & CClientUIInterface::BTN_MASK)))
             buttons = QMessageBox::Ok;
 
-        // Ensure we get users attention
-        showNormalIfMinimized();
+        // Ensure we get users attention, but only if main window is visible
+        // as we don't want to pop up the main window for messages that happen before
+        // initialization is finished.
+        if(!(style & CClientUIInterface::NOSHOWGUI))
+            showNormalIfMinimized();
         QMessageBox mBox((QMessageBox::Icon)nMBoxIcon, strTitle, message, buttons, this);
         int r = mBox.exec();
         if (ret != NULL)