Avoid spurious "maybe uninitialized" MSVC warnings

Always initialize the variables that were previously only initialized in
the case when they were really used -- this doesn't cost much and avoids
MSVC warnings about these variables being possibly uninitialized.

src/qt/bitmap.cpp

@@ -86,7 +86,7 @@ static QImage ConvertImage( const wxImage &image, wxMask** mask = nullptr  )
     QRgb colour;
 
     QImage qtMask;
-    QRgb maskedColour;
+    QRgb maskedColour wxDUMMY_INITIALIZE(0);
     if ( hasMask )
     {
         unsigned char r, g, b;

src/qt/font.cpp

@@ -522,7 +522,7 @@ void wxNativeFontInfo::SetPixelSize(const wxSize& size)
 
 void wxNativeFontInfo::SetStyle(wxFontStyle style)
 {
-    QFont::Style qtStyle;
+    QFont::Style qtStyle wxDUMMY_INITIALIZE(QFont::StyleNormal);
 
     switch ( style )
     {