avutil/opt: Fix AV_OPT_TYPE_CONST default value

It uses the int64_t instead of the double member.

(This code can currently not be reached: av_opt_get() calls
av_opt_find2() with NULL as unit in which case AV_OPT_TYPE_CONST
options are never returned, leading av_opt_get() to always
return AVERROR_OPTION_NOT_FOUND when searching for AV_OPT_TYPE_CONST*.
For the same reason the code read_number() will never be called
from get_number() when searching for an option of type
AV_OPT_TYPE_CONST. The other callers of read_number() also only
call it with types other than AV_OPT_TYPE_CONST.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavutil/opt.c

@@ -93,7 +93,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
         *den    = ((AVRational *)dst)->den;
         return 0;
     case AV_OPT_TYPE_CONST:
-        *num = o->default_val.dbl;
+        *intnum = o->default_val.i64;
         return 0;
     }
     return AVERROR(EINVAL);
@@ -878,7 +878,7 @@ int av_opt_get(void *obj, const char *name, int search_flags, uint8_t **out_val)
         ret = snprintf(buf, sizeof(buf), "%d/%d", ((AVRational *)dst)->num, ((AVRational *)dst)->den);
         break;
     case AV_OPT_TYPE_CONST:
-        ret = snprintf(buf, sizeof(buf), "%f", o->default_val.dbl);
+        ret = snprintf(buf, sizeof(buf), "%"PRId64, o->default_val.i64);
         break;
     case AV_OPT_TYPE_STRING:
         if (*(uint8_t **)dst) {