avcodec/libx264: fix "bitrate reconfiguration"

libavcodec/libx264.c

@@ -208,18 +208,20 @@ static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame,
         }
 
         if (x4->params.rc.i_rc_method == X264_RC_CRF &&
+            x4->crf >= 0 &&
             x4->params.rc.f_rf_constant != x4->crf) {
             x4->params.rc.f_rf_constant = x4->crf;
             x264_encoder_reconfig(x4->enc, &x4->params);
         }
 
         if (x4->params.rc.i_rc_method == X264_RC_CQP &&
+            x4->cqp >= 0 &&
             x4->params.rc.i_qp_constant != x4->cqp) {
             x4->params.rc.i_qp_constant = x4->cqp;
             x264_encoder_reconfig(x4->enc, &x4->params);
         }
 
-        if (x4->crf_max &&
+        if (x4->crf_max >= 0 &&
             x4->params.rc.f_rf_constant_max != x4->crf_max) {
             x4->params.rc.f_rf_constant_max = x4->crf_max;
             x264_encoder_reconfig(x4->enc, &x4->params);