fix stream class

fix a infinite loop on corrupted streams

Originally committed as revision 4344 to svn://svn.ffmpeg.org/ffmpeg/trunk

tests/libav.regression.ref

@@ -22,7 +22,7 @@ c85c98bb1c9a5fe833eed5d23fbf8499 *./data/b-libav.ffm
 55d26d5f682f75fa57a5c126056c4c31 *./data/b-libav.mov
 369865 ./data/b-libav.mov
 ./data/b-libav.mov CRC=48f5a90d
-f34e560f8f0f2c603cf0cb3e7eeb031b *./data/b-libav.nut
+ec525a567d12e43a0f485b60a270c496 *./data/b-libav.nut
 332415 ./data/b-libav.nut
 ./data/b-libav.nut CRC=ccab3a27
 29a2c312bbc5b187491183a918556475 *./data/b-libav.dv