bytestream2: set the reader to the end when reading more than available

This prevents possible infinite loops with the calling code along the
lines of while (bytestream2_get_bytes_left()) { ... }, where the reader
does not advance.

CC: libav-stable@libav.org
(cherry picked from commit 86eee85d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/bytestream.h

@@ -71,8 +71,10 @@ static av_always_inline type bytestream2_get_ ## name ## u(GetByteContext *g)  \
 }                                                                              \
 static av_always_inline type bytestream2_get_ ## name(GetByteContext *g)       \
 {                                                                              \
-    if (g->buffer_end - g->buffer < bytes)                                     \
+    if (g->buffer_end - g->buffer < bytes) {                                   \
+        g->buffer = g->buffer_end;                                             \
         return 0;                                                              \
+    }                                                                          \
     return bytestream2_get_ ## name ## u(g);                                   \
 }                                                                              \
 static av_always_inline type bytestream2_peek_ ## name(GetByteContext *g)      \