call OnInit() from all samples to allow using standard command line options with all of them (patch 1623971)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44354 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dragimag/dragimag.cpp

@@ -368,6 +368,9 @@ MyApp::MyApp()
 
 bool MyApp::OnInit()
 {
+    if ( !wxApp::OnInit() )
+        return false;
+
 #if wxUSE_LIBPNG
     wxImage::AddHandler( new wxPNGHandler );
 #endif