Make av_d2q() manage the case in which the value to convert is inf.

Originally committed as revision 25332 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/rational.c

@@ -100,6 +100,8 @@ AVRational av_d2q(double d, int max){
     int64_t den;
     if (isnan(d))
         return (AVRational){0,0};
+    if (isinf(d))
+        return (AVRational){ d<0 ? -1:1, 0 };
     exponent = FFMAX( (int)(log(fabs(d) + 1e-20)/LOG2), 0);
     den = 1LL << (61 - exponent);
     av_reduce(&a.num, &a.den, (int64_t)(d * den + 0.5), den, max);