windowscodecs: Add stub for DllCanUnloadNow.

dlls/windowscodecs/main.c

@@ -49,6 +49,11 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
     return WIC_DllMain(hinstDLL, fdwReason, lpvReserved);
 }
 
+HRESULT WINAPI DllCanUnloadNow(void)
+{
+    return S_FALSE;
+}
+
 HRESULT copy_pixels(UINT bpp, const BYTE *srcbuffer,
     UINT srcwidth, UINT srcheight, INT srcstride,
     const WICRect *rc, UINT dststride, UINT dstbuffersize, BYTE *dstbuffer)

dlls/windowscodecs/windowscodecs.spec

+@ stdcall -private DllCanUnloadNow()
 @ stdcall -private DllGetClassObject(ptr ptr ptr)
 @ stdcall -private DllRegisterServer()
 @ stdcall -private DllUnregisterServer()