Literal matching empty string buffer overflow

[danlark1]

In this issue it compiles but hs_scan fails under ASAN

#undef NDEBUG
#include <hs.h>
#include <cassert>

/*
Explanation: ASAN segfault.
Version: 5.4.0
==162837==ERROR: AddressSanitizer: global-buffer-overflow on address 0x00000140324e at pc 0x0000005047a8 bp 0x7ffc2fc1f4d0 sp 0x7ffc2fc1f4c8
READ of size 4 at 0x00000140324e thread T0
    #0 0x5047a7 in unaligned_load_u32 contrib/hyperscan/src/util/unaligned.h:58:18
    #1 0x5047a7 in masked_move256_len contrib/hyperscan/src/util/masked_move.h:70:15
    #2 0x5047a7 in scanDoubleShort contrib/hyperscan/src/hwlm/noodle_engine_avx2.c:165:13
    #3 0x5047a7 in scanDoubleMain contrib/hyperscan/src/hwlm/noodle_engine.c:239:14
    #4 0x5047a7 in scanDoubleCase contrib/hyperscan/src/hwlm/noodle_engine.c:341:12
    #5 0x5047a7 in scanDouble contrib/hyperscan/src/hwlm/noodle_engine.c:352:16
    #6 0x5047a7 in scan contrib/hyperscan/src/hwlm/noodle_engine.c:369:16
    #7 0x5047a7 in noodExec contrib/hyperscan/src/hwlm/noodle_engine.c:383:12
    #8 0x4d207f in pureLiteralBlockExec contrib/hyperscan/src/runtime.c:218:5
    #9 0x4d207f in hs_scan contrib/hyperscan/src/runtime.c:422:9
    #10 0x4d0cce in main hyperscan_bugs/empty_string_buffer_overflow.cpp:59:11
    #11 0x7f682e4f3d09 in __libc_start_main csu/../csu/libc-start.c:308:16
    #12 0x4243c9 in _start (build_asan/hyperscan_bugs/empty_string_buffer_overflow+0x4243c9)
*/

int on_match(unsigned int id,
             unsigned long long from,
             unsigned long long to,
             unsigned int /* flags */,
             void * context) {
    return 0;
}

int main() {
    hs_database_t *db = nullptr;
    hs_compile_error_t *compile_err = nullptr;
    // Haystack:
    const char* data = "\xb1\xb1\x0a\xb1\xb1\x0a\x0a\x0a\x0a\x0a\x00\x00\x00";
    const size_t size = 13;
    // Patterns:
    const char *expr[] = {
        "",
        "",
    };
    unsigned ids[] = {0, 1};
    size_t lens[] = {0, 0};
    unsigned flags[] = {HS_FLAG_SINGLEMATCH, HS_FLAG_SOM_LEFTMOST};
    hs_error_t err = hs_compile_lit_multi(expr, flags, ids, lens, sizeof(ids)/sizeof(*ids), HS_MODE_BLOCK, nullptr, &db, &compile_err);

    assert(HS_SUCCESS == err);
    assert(db != nullptr);
        hs_scratch_t *scratch = nullptr;
    err = hs_alloc_scratch(db, &scratch);
    assert(HS_SUCCESS == err);
    assert(scratch != nullptr);

    err = hs_scan(db, data, size, 0, scratch, on_match, nullptr);
    assert(HS_SUCCESS == err);

    hs_free_database(db);
    err = hs_free_scratch(scratch);
    assert(HS_SUCCESS == err);
}

[Nor7th]

Similar to fix for #302

[hongyang7]

Please refer to latest develop branch.