Fix problem initializing SkiaDisplay with an invalid surface size on OS X

This problem happened when Aseprite is run for the very first time on OS X
(i.e. without an aseprite.ini file in the user configuration directory),
as the final size of the created window might be different (smaller) than
the given width/height parameters in the SkiaDisplay constructor.

src/she/skia/skia_display.cpp

@@ -24,11 +24,11 @@ SkiaDisplay::SkiaDisplay(int width, int height, int scale)
   , m_customSurface(false)
   , m_nativeCursor(kArrowCursor)
 {
-  m_surface->create(width / scale,
-                    height / scale);
   m_window.setScale(scale);
   m_window.setVisible(true);
 
+  resetSkiaSurface();
+
   m_initialized = true;
 }