Fix support for flvtool2 "keyframes based" generated index in FLV format decoder

Current keyframes data parser unconditionally rewind metadata to the end
at the end of function. As result ALL metadata located after keyframes
index not parsed,
and as metadata object can have ANY placement inside metadata it can
lead to unpredictable result
(bitrate can not be found, etc.). As result FLV movie will not play at
all in such situation.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/flvdec.c

@@ -131,6 +131,7 @@ static int parse_keyframes_index(AVFormatContext *s, AVIOContext *ioc, AVStream
     int64_t *times = NULL;
     int64_t *filepositions = NULL;
     int ret = 0;
+    int64_t initial_pos = url_ftell(ioc);
 
     while (avio_tell(ioc) < max_pos - 2 && amf_get_string(ioc, str_val, sizeof(str_val)) > 0) {
         int64_t** current_array;
@@ -174,7 +175,7 @@ static int parse_keyframes_index(AVFormatContext *s, AVIOContext *ioc, AVStream
 finish:
     av_freep(&times);
     av_freep(&filepositions);
-    avio_seek(ioc, max_pos, SEEK_SET);
+    avio_seek(ioc, initial_pos, SEEK_SET);
     return ret;
 }