Make sure rtjpeg quality is a valid value

Originally committed as revision 10444 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/nuv.c

@@ -97,6 +97,7 @@ static int get_quant(AVCodecContext *avctx, NuvContext *c,
  */
 static void get_quant_quality(NuvContext *c, int quality) {
     int i;
+    quality = FFMAX(quality, 1);
     for (i = 0; i < 64; i++) {
         c->lq[i] = (fallback_lquant[i] << 7) / quality;
         c->cq[i] = (fallback_cquant[i] << 7) / quality;