lavfi/vf_drawtext.c: fix CID 1485003

CID 1485003: Memory - illegal accesses (UNINIT)
Using uninitialized value "sd".

Signed-off-by: Ting Fu <ting.fu@intel.com>

libavfilter/vf_drawtext.c

@@ -1554,7 +1554,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
     AVFrameSideData *sd;
     int loop = 1;
 
-    if (s->text_source == AV_FRAME_DATA_DETECTION_BBOXES && sd) {
+    if (s->text_source == AV_FRAME_DATA_DETECTION_BBOXES) {
         sd = av_frame_get_side_data(frame, AV_FRAME_DATA_DETECTION_BBOXES);
         if (sd) {
             header = (AVDetectionBBoxHeader *)sd->data;