avcodec/mjpegdec: Dont skip picture allocation if theres no picture allocated

Fixes Ticket 3245

libavcodec/mjpegdec.c

@@ -336,7 +336,7 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
         s->first_picture = 0;
     }
 
-    if (s->interlaced && (s->bottom_field == !s->interlace_polarity)) {
+    if (s->got_picture && s->interlaced && (s->bottom_field == !s->interlace_polarity)) {
         if (s->progressive) {
             avpriv_request_sample(s->avctx, "progressively coded interlaced picture");
             return AVERROR_INVALIDDATA;