mpeg4audio: Fix a crash with some invalid streams.

If rate stays at 0, a FPE will be raised in SetupOutput.
(cherry picked from commit f5bc59c5)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/packetizer/mpeg4audio.c

@@ -808,6 +808,9 @@ static int LOASParse( decoder_t *p_dec, uint8_t *p_buffer, int i_buffer )
             p_sys->i_rate = st->cfg.i_samplerate;
             p_sys->i_frame_length = st->cfg.i_frame_length;
 
+            if ( p_sys->i_channels > 0 && p_sys->i_rate > 0 &&
+                 p_sys->i_frame_length > 0 )
+            {
                 /* FIXME And if it changes ? */
                 if( !p_dec->fmt_out.i_extra && st->i_extra > 0 )
                 {
@@ -820,10 +823,10 @@ static int LOASParse( decoder_t *p_dec, uint8_t *p_buffer, int i_buffer )
                     }
                     memcpy( p_dec->fmt_out.p_extra, st->extra, st->i_extra );
                 }
-
                 p_sys->b_latm_cfg = true;
             }
         }
+    }
     /* Wait for the configuration */
     if( !p_sys->b_latm_cfg )
         return 0;