avcodec/ac3dec: Reset SPX when switching from EAC3 to AC3

Fixes Ticket5319
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ac3dec.c

@@ -895,13 +895,15 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
                                   ff_eac3_default_spx_band_struct,
                                   &s->num_spx_bands,
                                   s->spx_band_sizes);
-        } else {
+        }
+    }
+    if (!s->eac3 || !s->spx_in_use) {
+        s->spx_in_use = 0;
         for (ch = 1; ch <= fbw_channels; ch++) {
             s->channel_uses_spx[ch] = 0;
             s->first_spx_coords[ch] = 1;
         }
     }
-    }
 
     /* spectral extension coordinates */
     if (s->spx_in_use) {