avformat/movenc: shift positive timestamps to 0 if edit lists cannot be used

Fix handling of timestamps which start  far away from 0
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/movenc.c

@@ -3761,7 +3761,7 @@ static int mov_write_header(AVFormatContext *s)
     }
 
     if (!supports_edts(mov) && s->avoid_negative_ts < 0) {
-        s->avoid_negative_ts = 1;
+        s->avoid_negative_ts = 2;
     }
 
     /* Non-seekable output is ok if using fragmentation. If ism_lookahead

tests/ref/fate/sub-movtextenc

-8cb21f3632e1c86358429fb9402d19d4
+cf3d43e6de1f97681583ba08d9fe5938

tests/ref/lavf/ismv

-ec3e7d37755378cbe9907175768afbac *./tests/data/lavf/lavf.ismv
+df243ab73b33905776bdaefb79d14be8 *./tests/data/lavf/lavf.ismv
 312453 ./tests/data/lavf/lavf.ismv
-./tests/data/lavf/lavf.ismv CRC=0x9d9a638a
-a4b6fb1f46848622477230f69040942c *./tests/data/lavf/lavf.ismv
+./tests/data/lavf/lavf.ismv CRC=0xb7d29d29
+c40d80b3b35c9cd1324dead65dfcdb69 *./tests/data/lavf/lavf.ismv
 321359 ./tests/data/lavf/lavf.ismv
-./tests/data/lavf/lavf.ismv CRC=0xe8130120
-ec3e7d37755378cbe9907175768afbac *./tests/data/lavf/lavf.ismv
+./tests/data/lavf/lavf.ismv CRC=0x33834815
+df243ab73b33905776bdaefb79d14be8 *./tests/data/lavf/lavf.ismv
 312453 ./tests/data/lavf/lavf.ismv
-./tests/data/lavf/lavf.ismv CRC=0x9d9a638a
+./tests/data/lavf/lavf.ismv CRC=0xb7d29d29