Fix GH-15980: Signed integer overflow in main/streams/streams.c

We need to avoid signed integer overflows which are undefined behavior.
We catch that, and set `offset` to `ZEND_LONG_MAX`

Fix GH-15980: Signed integer overflow in main/streams/streams.c

We need to avoid signed integer overflows which are undefined behavior.
We catch that, and set `offset` to `ZEND_LONG_MAX` (which is also the
largest value of `zend_off_t` on all platforms). Of course, that seek
may fail, but even if it succeeds, the stream is no longer readable,
but that matches the current behavior for offsets near `ZEND_LONG_MAX`.

Closes GH-15989.

show more ...