Fix heap-buffer-overflow in Swift tree-sitter scanner

The Swift external scanner called calloc(0, sizeof(ScannerState)) which
returns a 0-or-1-byte allocation per the C standard. The scanner then
writes a uint32_t (4 bytes) to this region via state->ongoing_raw_str_hash_count,
causing a heap-buffer-overflow detected by AddressSanitizer.

Fix: calloc(0, ...) → calloc(1, ...).

Author: DeusData