vorbisdec: Check that the x values of floor1 are unique.

This is required by the spec and fixes video-1frag.ogg.48.ogg. (FPE)

Based on the debuging work of Oana Stratulat and ubitux.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vorbisdec.c

@@ -579,6 +579,14 @@ static int vorbis_parse_setup_hdr_floors(vorbis_context *vc)
 
 // Precalculate order of x coordinates - needed for decode
             ff_vorbis_ready_floor1_list(floor_setup->data.t1.list, floor_setup->data.t1.x_list_dim);
+
+            for (j=1; j<floor_setup->data.t1.x_list_dim; j++) {
+                if (   floor_setup->data.t1.list[ floor_setup->data.t1.list[j-1].sort ].x
+                    == floor_setup->data.t1.list[ floor_setup->data.t1.list[j  ].sort ].x) {
+                    av_log(vc->avccontext, AV_LOG_ERROR, "Non unique x values in floor type 1\n");
+                    return AVERROR_INVALIDDATA;
+                }
+            }
         } else if (floor_setup->floor_type == 0) {
             unsigned max_codebook_dim = 0;