Fixed crash if initialization of EGL failed but was tried again later.

The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().

src/main/winrt/SDL_winrt_main_NonXAML.cpp

@@ -0,0 +1,59 @@
+/*
+    SDL_winrt_main_NonXAML.cpp, placed in the public domain by David Ludwig  3/13/14
+*/
+
+#include "SDL_main.h"
+#include <wrl.h>
+
+/* At least one file in any SDL/WinRT app appears to require compilation
+   with C++/CX, otherwise a Windows Metadata file won't get created, and
+   an APPX0702 build error can appear shortly after linking.
+
+   The following set of preprocessor code forces this file to be compiled
+   as C++/CX, which appears to cause Visual C++ 2012's build tools to
+   create this .winmd file, and will help allow builds of SDL/WinRT apps
+   to proceed without error.
+
+   If other files in an app's project enable C++/CX compilation, then it might
+   be possible for SDL_winrt_main_NonXAML.cpp to be compiled without /ZW,
+   for Visual C++'s build tools to create a winmd file, and for the app to
+   build without APPX0702 errors.  In this case, if
+   SDL_WINRT_METADATA_FILE_AVAILABLE is defined as a C/C++ macro, then
+   the #error (to force C++/CX compilation) will be disabled.
+
+   Please note that /ZW can be specified on a file-by-file basis.  To do this,
+   right click on the file in Visual C++, click Properties, then change the
+   setting through the dialog that comes up.
+*/
+#ifndef SDL_WINRT_METADATA_FILE_AVAILABLE
+#ifndef __cplusplus_winrt
+#error SDL_winrt_main_NonXAML.cpp must be compiled with /ZW, otherwise build errors due to missing .winmd files can occur.
+#endif
+#endif
+
+/* Prevent MSVC++ from warning about threading models when defining our
+   custom WinMain.  The threading model will instead be set via a direct
+   call to Windows::Foundation::Initialize (rather than via an attributed
+   function).
+
+   To note, this warning (C4447) does not seem to come up unless this file
+   is compiled with C++/CX enabled (via the /ZW compiler flag).
+*/
+#ifdef _MSC_VER
+#pragma warning(disable:4447)
+#endif
+
+/* Make sure the function to initialize the Windows Runtime gets linked in. */
+#ifdef _MSC_VER
+#pragma comment(lib, "runtimeobject.lib")
+#endif
+
+int CALLBACK WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
+{
+    if (FAILED(Windows::Foundation::Initialize(RO_INIT_MULTITHREADED))) {
+        return 1;
+    }
+
+    SDL_WinRTRunApp(SDL_main, NULL);
+    return 0;
+}