gstplugin: Don't stat plugins when building for UWP

When using GStreamer with Universal Windows Platform apps, dynamic
plugins can only be loaded by filename (without a path) using
gst_plugin_load_file() which will call into g_module_open().

On Windows, GModule calls LoadLibrary() on the filename, but with
UWP we need to use LoadPackagedLibrary() which is basically the same
as LoadLibrary(), except it looks only for DLLs (by name) that have
been packaged as assets with the app.

These assets are not files and cannot be accessed using normal file
APIs such as open() or stat().

The upstream glib merge request for adding LoadPackagedLibrary support
is: https://gitlab.gnome.org/GNOME/glib/merge_requests/951

NOTE: Whitespcae removal is to make gst-indent happy

gst/gstplugin.c

@@ -69,6 +69,13 @@
 
 #include <gst/gst.h>
 
+#ifdef G_OS_WIN32
+#include <windows.h>
+#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP) && !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+#define GST_WINAPI_ONLY_APP
+#endif
+#endif
+
 #define GST_CAT_DEFAULT GST_CAT_PLUGIN_LOADING
 
 static guint _num_static_plugins;       /* 0    */
@@ -767,7 +774,12 @@ _priv_gst_plugin_load_file_for_registry (const gchar * filename,
         GST_PLUGIN_ERROR_MODULE, "Dynamic loading not supported");
     goto return_error;
   }
-
+#if defined(GST_WINAPI_ONLY_APP)
+  /* plugins loaded by filename by Universal Windows Platform apps do not use
+   * an actual file with a path, they use a packaged (asset) library */
+  file_status.st_mtime = 0;
+  file_status.st_size = 0;
+#else
   if (g_stat (filename, &file_status)) {
     GST_CAT_DEBUG (GST_CAT_PLUGIN_LOADING, "problem accessing file");
     g_set_error (error,
@@ -776,6 +788,7 @@ _priv_gst_plugin_load_file_for_registry (const gchar * filename,
         g_strerror (errno));
     goto return_error;
   }
+#endif
 
   flags = G_MODULE_BIND_LOCAL;
   /* libgstpython.so is the gst-python plugin loader. It needs to be loaded with