Use gdk_threads_enter/gdk_threads_leave to ensure gtk multithread safe

If the video player tries to play an unknown type file, it will enter
the error_cb() function, which is called in another thread.
Use gdk_threads_enter/gdk_threads_leave to ensure the safe of gtk
multi-thread operation.

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>

diff -ruN video-orig/src/video.c video/src/video.c
--- video-orig/src/video.c	2010-10-15 16:07:26.522346398 +0800
+++ video/src/video.c	2010-10-15 16:25:51.780296717 +0800
@@ -96,6 +96,7 @@
 {
         GtkWidget *dialog;
 
+        gdk_threads_enter();
         dialog = gtk_message_dialog_new (data->window,
                                          GTK_DIALOG_NO_SEPARATOR,
                                          GTK_MESSAGE_ERROR,
@@ -103,6 +104,7 @@
                                          error->message);
         gtk_dialog_run (GTK_DIALOG (dialog));
         gtk_widget_destroy (dialog);
+        gdk_threads_leave();
 }
 
 /**
@@ -606,7 +608,9 @@
         
         gtk_widget_show_all (GTK_WIDGET (data->window));
 
+        gdk_threads_enter();
         gtk_main ();
+        gdk_threads_leave();
 
         /**
          * Cleanup.