* prevent crashes when a stream is not opened correctly

include/vlc_stream.h

@@ -123,6 +123,9 @@ static inline int stream_Control( stream_t *s, int i_query, ... )
     va_list args;
     int     i_result;
 
+    if ( s == NULL )
+        return VLC_EGENERIC;
+
     va_start( args, i_query );
     i_result = s->pf_control( s, i_query, args );
     va_end( args );

modules/demux/mkv.cpp

@@ -1481,10 +1481,14 @@ static int Open( vlc_object_t * p_this )
 #endif
                     {
                         // test wether this file belongs to our family
-                        vlc_stream_io_callback *p_file_io = new vlc_stream_io_callback( stream_UrlNew( p_demux, s_filename.c_str()), VLC_TRUE );
+                        stream_t *p_file_stream = stream_UrlNew( p_demux, s_filename.c_str());
+                        if ( p_file_stream != NULL )
+                        {
+                            vlc_stream_io_callback *p_file_io = new vlc_stream_io_callback( p_file_stream, VLC_TRUE );
                             EbmlStream *p_estream = new EbmlStream(*p_file_io);
 
                             p_stream = p_sys->AnalyseAllSegmentsFound( p_estream );
+
                             if ( p_stream == NULL )
                             {
                                 msg_Dbg( p_demux, "the file '%s' will not be used", s_filename.c_str() );
@@ -1498,6 +1502,11 @@ static int Open( vlc_object_t * p_this )
                                 p_sys->streams.push_back( p_stream );
                             }
                         }
+                        else
+                        {
+                            msg_Dbg( p_demux, "the file '%s' cannot be opened", s_filename.c_str() );
+                        }
+                    }
                 }
             }
             closedir( p_src_dir );
@@ -3324,6 +3333,8 @@ size_t vlc_stream_io_callback::write( const void *p_buffer, size_t i_size )
 }
 uint64 vlc_stream_io_callback::getFilePointer( void )
 {
+    if ( s == NULL )
+        return 0;
     return stream_Tell( s );
 }
 void vlc_stream_io_callback::close( void )