Check malloc return value.

src/stream_output/stream_output.c

@@ -520,6 +520,11 @@ sout_input_t *sout_MuxAddStream( sout_mux_t *p_mux, es_format_t *p_fmt )
 
     /* create a new sout input */
     p_input = malloc( sizeof( sout_input_t ) );
+    if( !p_input )
+    {
+        msg_Err( p_mux, "out of memory" );
+        return NULL;
+    }
     p_input->p_sout = p_mux->p_sout;
     p_input->p_fmt  = p_fmt;
     p_input->p_fifo = block_FifoNew( p_mux->p_sout );