Description:
------------
When calling `mb_ereg_search_setpos` with the end position of a string as argument, it raises a warning and returns false and resets the search position to zero.

This prevents `mb_ereg_search` to match at the end of the string (for example zero-width assertions like '\Z', '$' or lookbehinds).

The correct behavior should be to not throw a warning, and set the position accordingly.

What's more, once you call `mb_ereg_search_setpos(strlen($str))`, the `mb_ereg_search` behavior seems to be erratic, see the test script, where the '\Z' assertion matches and sets position to 3 eventhough `mb_ereg_search_getpos` just returned 0 !

Test script:
---------------
mb_ereg_search_init('foo');

var_dump(mb_ereg_search_setpos(3));
var_dump(mb_ereg_search_getpos());

var_dump(mb_ereg_search('\Z'));
var_dump(mb_ereg_search_getpos());

Expected result:
----------------
bool(true)
int(3)

bool(true)
int(3)

Actual result:
--------------
Warning: mb_ereg_search_setpos(): Position is out of range in ...
bool(false)
int(0)

Warning: mb_ereg_search(): Empty regular expression in ...
bool(true)
int(3)