avformat/fitsdec: Fix potential leak of string in AVBPrint

by freeing it a bit earlier.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/fitsdec.c

@@ -157,11 +157,11 @@ static int fits_read_packet(AVFormatContext *s, AVPacket *pkt)
 
     av_bprint_init(&avbuf, FITS_BLOCK_SIZE, AV_BPRINT_SIZE_UNLIMITED);
     while ((ret = is_image(s, fits, &header, &avbuf, &size)) == 0) {
+        av_bprint_finalize(&avbuf, NULL);
         pos = avio_skip(s->pb, size);
         if (pos < 0)
             return pos;
 
-        av_bprint_finalize(&avbuf, NULL);
         av_bprint_init(&avbuf, FITS_BLOCK_SIZE, AV_BPRINT_SIZE_UNLIMITED);
         avpriv_fits_header_init(&header, STATE_XTENSION);
     }