Stop the approximation in bessel() once it does no longer improve.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@21038 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/resample2.c

@@ -76,11 +76,13 @@ typedef struct AVResampleContext{
  */
 static double bessel(double x){
     double v=1;
+    double lastv=0;
     double t=1;
     int i;
 
     x= x*x/4;
-    for(i=1; i<50; i++){
+    for(i=1; v != lastv; i++){
+        lastv=v;
         t *= x/(i*i);
         v += t;
     }