avutil/opt: only skip evaluation for rational options

Fixes problems when non-rational options were set using rational expressions,
causing rounding errors and the option range limits not to be enforced
properly.

ffmpeg -f lavfi -i "sine=r=96000/2"

This caused an assertion failure with assert level 2.
Signed-off-by: Marton Balint <cus@passwd.hu>

libavutil/opt.c

@@ -229,13 +229,15 @@ static int set_string(void *obj, const AVOption *o, const char *val, uint8_t **d
 static int set_string_number(void *obj, void *target_obj, const AVOption *o, const char *val, void *dst)
 {
     int ret = 0;
-    int num, den;
-    char c;
 
-    if (sscanf(val, "%d%*1[:/]%d%c", &num, &den, &c) == 2) {
-        if ((ret = write_number(obj, o, dst, 1, den, num)) >= 0)
-            return ret;
-        ret = 0;
+    if (o->type == AV_OPT_TYPE_RATIONAL || o->type == AV_OPT_TYPE_VIDEO_RATE) {
+        int num, den;
+        char c;
+        if (sscanf(val, "%d%*1[:/]%d%c", &num, &den, &c) == 2) {
+            if ((ret = write_number(obj, o, dst, 1, den, num)) >= 0)
+                return ret;
+            ret = 0;
+        }
     }
 
     for (;;) {