fix seek regression tests after r15229

The matroska demuxer now index every streams so seek on stream 1 now works.

Originally committed as revision 15254 to svn://svn.ffmpeg.org/ffmpeg/trunk

tests/seek.regression.ref

@@ -2966,7 +2966,7 @@ ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st: 1 ts:2.577000 flags:0
 ret:-5
 ret: 0 st: 1 ts:1.471000 flags:1
-ret:-5
+ret: 0 st: 1 dts:0.000000 pts:0.000000 pos:28603 size:208 flags:1
 ret: 0 st:-1 ts:0.365002 flags:0
 ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st:-1 ts:-0.740831 flags:1
@@ -2976,9 +2976,9 @@ ret:-5
 ret: 0 st: 0 ts:1.048000 flags:1
 ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st: 1 ts:-0.058000 flags:0
-ret:-5
+ret: 0 st: 1 dts:0.000000 pts:0.000000 pos:28603 size:208 flags:1
 ret: 0 st: 1 ts:2.836000 flags:1
-ret:-5
+ret: 0 st: 1 dts:0.000000 pts:0.000000 pos:28603 size:208 flags:1
 ret: 0 st:-1 ts:1.730004 flags:0
 ret:-5
 ret: 0 st:-1 ts:0.624171 flags:1
@@ -2990,7 +2990,7 @@ ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st: 1 ts:1.307000 flags:0
 ret:-5
 ret: 0 st: 1 ts:0.201000 flags:1
-ret:-5
+ret: 0 st: 1 dts:0.000000 pts:0.000000 pos:28603 size:208 flags:1
 ret: 0 st:-1 ts:-0.904994 flags:0
 ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st:-1 ts:1.989173 flags:1
@@ -3002,7 +3002,7 @@ ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st: 1 ts:2.672000 flags:0
 ret:-5
 ret: 0 st: 1 ts:1.566000 flags:1
-ret:-5
+ret: 0 st: 1 dts:0.000000 pts:0.000000 pos:28603 size:208 flags:1
 ret: 0 st:-1 ts:0.460008 flags:0
 ret: 0 st: 0 dts:0.000000 pts:0.000000 pos:478 size:28118 flags:1
 ret: 0 st:-1 ts:-0.645825 flags:1