[php-src] PR #24419: Fix GH-24397: Clear vacated MERGE inputs in _zend_jit_fix_merges()

Pull Request: https://github.com/php/php-src/pull/24419 Author: iliaal _zend_jit_fix_merges() compacts a MERGE's live inputs to the left without clearing the slots it vacates. When one input survives, the node becomes a BEGIN whose op2 is a label operand, so the stale END ref is read as a label: ir_save() asserts on it in debug builds when opcache.jit_debug sets an IR dump bit, and in all builds the aliasing load and store searches treat the block as address-taken and stop there. PHI compaction reads only up to inputs_count, and the PHI-to-COPY conversion already overwrites op2. Fixes #24397