Description:
------------
array_rand doesn't return array but a key as string when 
given mixed array which has only one value(and key).

Reproduce code:
---------------
$array = array("test");
$rand_key = array_rand($array, count($array));
print_r($rand_key);

print("\n");

$array2 = array("test" => "value");
$rand_key2 = array_rand($array2, count($array2));
print_r($rand_key2);

print("\n");

$array3 = array("test" => "value", "test2" => "value2");
$rand_key3 = array_rand($array3, count($array3));
print_r($rand_key3);

print("\n"); 

Expected result:
----------------
Array([0] => 0)
Array([0] => test)
Array
(
    [0] => test
    [1] => test2
)
*the last one is right. Above two are not expected 
result.

Actual result:
--------------
0
test
Array
(
    [0] => test
    [1] => test2
)