avcodec/mjpegdec: Fix decoding slightly odd progressive jpeg

Fixes: ebd58db6-dc86-11e5-91c2-59daeddf50c7.jpg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mjpegdec.c

@@ -1381,12 +1381,10 @@ static int mjpeg_decode_scan_progressive_ac(MJpegDecodeContext *s, int ss,
         return AVERROR_INVALIDDATA;
     }
 
-    if (!Al) {
     // s->coefs_finished is a bitmask for coefficients coded
     // ss and se are parameters telling start and end coefficients
     s->coefs_finished[c] |= (2ULL << se) - (1ULL << ss);
-        last_scan = !~s->coefs_finished[c];
-    }
+    last_scan = !Al && !~s->coefs_finished[c];
 
     if (s->interlaced && s->bottom_field)
         data += linesize >> 1;