lavf/mpegts: Return small probe score for very short transport streams.

Fixes Debian bug 823098.

(cherry picked from commit 88a849c714)

libavformat/mpegts.c

@@ -2441,7 +2441,7 @@ static int mpegts_probe(AVProbeData *p)
 #define CHECK_COUNT 10
 #define CHECK_BLOCK 100
 
-    if (check_count < CHECK_COUNT)
+    if (!check_count)
         return 0;
 
     for (i = 0; i<check_count; i+=CHECK_BLOCK) {
@@ -2459,10 +2459,15 @@ static int mpegts_probe(AVProbeData *p)
 
     ff_dlog(0, "TS score: %d %d\n", sumscore, maxscore);
 
-    if      (sumscore > 6) return AVPROBE_SCORE_MAX   + sumscore - CHECK_COUNT;
-    else if (maxscore > 6) return AVPROBE_SCORE_MAX/2 + sumscore - CHECK_COUNT;
-    else
+    if        (check_count >= CHECK_COUNT && sumscore > 6) {
+        return AVPROBE_SCORE_MAX   + sumscore - CHECK_COUNT;
+    } else if (check_count >= CHECK_COUNT && maxscore > 6) {
+        return AVPROBE_SCORE_MAX/2 + sumscore - CHECK_COUNT;
+    } else if (sumscore > 6) {
+        return 2;
+    } else {
         return 0;
+    }
 }
 
 /* return the 90kHz PCR and the extension for the 27MHz PCR. return