rand(beginless_range) raise Errno::EDOM instead of TypeError

same as `rand(endless_range)`

Before:
```
$ ruby -e 'rand(..1)'
Traceback (most recent call last):
	2: from -e:1:in `<main>'
	1: from -e:1:in `rand'
-e:1:in `-': nil can't be coerced into Integer (TypeError)
```

After:
```
$ ruby -e 'rand(..1)'
Traceback (most recent call last):
	1: from -e:1:in `<main>'
-e:1:in `rand': Numerical argument out of domain (Errno::EDOM)
```

1 files changed, 4 insertions, 2 deletions

diff --git a/random.c b/random.c
index f72abb0a6c..68b47bcf1b 100644
--- a/random.c
+++ b/random.c
@@ -1043,9 +1043,11 @@ random_s_bytes(VALUE obj, VALUE len)
 static VALUE
 range_values(VALUE vmax, VALUE *begp, VALUE *endp, int *exclp)
 {
-    VALUE end;
+    VALUE beg, end;
 
-    if (!rb_range_values(vmax, begp, &end, exclp)) return Qfalse;
+    if (!rb_range_values(vmax, &beg, &end, exclp)) return Qfalse;
+    if (begp) *begp = beg;
+    if (NIL_P(beg)) return Qnil;
     if (endp) *endp = end;
     if (NIL_P(end)) return Qnil;
     return rb_check_funcall_default(end, id_minus, 1, begp, Qfalse);