Description:
------------
I was evaluating a variable with isset. I don't know what kind of variable it is before evaluating.

If I do a isset of a key of an array, and the variable is NOT an array, I receive a true response. I think this is not a good result.

Reproduce code:
---------------
function verify($var) {
  if (isset($var['key'])) {
    echo "OK";
  } else {
    echo "NO";
  }
  return;
}

verify ('asdfghjkl');
verify (array('key'=>'1', 'option'=>'2');
verify (array('action'=>'1', 'option'=>'2');

Expected result:
----------------
## verify ('asdfghjkl');
NO

## verify (array('key'=>'1', 'option'=>'2');
OK

## verify (array('action'=>'1', 'option'=>'2');
NO

Actual result:
--------------
## verify ('asdfghjkl');
OK

## verify (array('key'=>'1', 'option'=>'2');
OK

## verify (array('action'=>'1', 'option'=>'2');
NO