Fix GH-20964, GH-20927: fseek() stream seek with PHP_INT_MIN causes undefined behavior

[iliaal]

Summary

Stream seek functions in memory, pdo_sqlite, and sqlite3 compute the absolute value of a negative offset using (size_t)(-offset). When offset == ZEND_LONG_MIN, the signed negation overflows -- undefined behavior caught by UBSAN.

The fix swaps the cast order: -(size_t)offset casts to unsigned first (well-defined), then negates (well-defined unsigned arithmetic). Same result for all values, no behavioral change.

Files changed

• main/streams/memory.c -- php://memory and php://temp stream seek
• ext/pdo_sqlite/pdo_sqlite.c -- PDO SQLite blob stream seek
• ext/sqlite3/sqlite3.c -- SQLite3 blob stream seek

Existing PRs

• PR Fix fseek undefined behavior #20965 for UBSAN: fseek() on php://memory with PHP_INT_MIN causes undefined behavior #20964 uses the same cast-order fix but only covers memory streams
• PR Fixed negation of PHP_INT_MIN in ext/pdo_sqlite/pdo_sqlite.c #20928 for UBSan: negation of LONG_MIN in ext/pdo_sqlite/pdo_sqlite.c leads to undefined behavior #20927 uses the same cast-order fix but only covers pdo_sqlite

This patch covers all three affected files.

Fixes#20964
Fixes#20927

[Girgias]

I think this is fine, but @ndossche you also know the confusing rules around UB a bit better than I do.