Set wxGauge initial value correctly in wxQt

The default value of QProgressBar is -1, while wxGauge initial value
must be 0, so set it explicitly to fix a unit test failure with wxQt.

Closes https://github.com/wxWidgets/wxWidgets/pull/1043

src/qt/gauge.cpp

@@ -58,6 +58,7 @@ bool wxGauge::Create(wxWindow *parent,
     m_qtProgressBar->setOrientation( wxQtConvertOrientation( style, wxGA_HORIZONTAL ));
     m_qtProgressBar->setRange( 0, range );
     m_qtProgressBar->setTextVisible( style & wxGA_TEXT );
+    m_qtProgressBar->setValue(0);
 
     return QtCreateControl( parent, id, pos, size, style, validator, name );
 }