vcodec/vc1: compute rangex/y only for P/B frames

Fixes: left shift of 1073741824 by 1 places cannot be represented in type 'int'
Fixes: 16976/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1_fuzzer-4847262047404032

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vc1.c

@@ -1319,16 +1319,17 @@ int ff_vc1_parse_frame_header_adv(VC1Context *v, GetBitContext* gb)
         break;
     }
 
-    if (v->fcm != PROGRESSIVE && !v->s.quarter_sample) {
-        v->range_x <<= 1;
-        v->range_y <<= 1;
-    }
 
     /* AC Syntax */
     v->c_ac_table_index = decode012(gb);
     if (v->s.pict_type == AV_PICTURE_TYPE_I || v->s.pict_type == AV_PICTURE_TYPE_BI) {
         v->y_ac_table_index = decode012(gb);
     }
+    else if (v->fcm != PROGRESSIVE && !v->s.quarter_sample) {
+        v->range_x <<= 1;
+        v->range_y <<= 1;
+    }
+
     /* DC Syntax */
     v->s.dc_table_index = get_bits1(gb);
     if ((v->s.pict_type == AV_PICTURE_TYPE_I || v->s.pict_type == AV_PICTURE_TYPE_BI)