avformat/ftp: Check for av_strtok() failure

Fixes: CID1396258 Dereference null return value

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9d40782088)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/ftp.c

@@ -941,6 +941,8 @@ static int ftp_parse_entry_mlsd(char *mlsd, AVIODirEntry *next)
             continue;
         }
         fact = av_strtok(fact, "=", &value);
+        if (!fact)
+            continue;
         if (!av_strcasecmp(fact, "type")) {
             if (!av_strcasecmp(value, "cdir") || !av_strcasecmp(value, "pdir"))
                 return 1;