avutil/opt: handle whole range of int64_t in av_opt_get_int

Make get_int/set_int symetric. The int64_t to double to int64_t
conversion is unprecise for large value.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/opt.c

@@ -920,7 +920,10 @@ int av_opt_get_int(void *obj, const char *name, int search_flags, int64_t *out_v
 
     if ((ret = get_number(obj, name, NULL, &num, &den, &intnum, search_flags)) < 0)
         return ret;
-    *out_val = num * intnum / den;
+    if (num == den)
+        *out_val = intnum;
+    else
+        *out_val = num * intnum / den;
     return 0;
 }