Fix out-of-bounds write in the jerry-snapshot literals-list parser

[PGZXB]

process_generate() in the jerry-snapshot tool reads the literal entries of a
--load-literals-list-format file into two fixed-size globals,
magic_string_items[JERRY_LITERAL_LENGTH] and
magic_string_lengths[JERRY_LITERAL_LENGTH] (JERRY_LITERAL_LENGTH is 4096).
The parse loop increments num_of_lit for every entry with a positive size but
never checks it against the array capacity, so the 4097th entry writes
magic_string_items[4096] and magic_string_lengths[4096] past the end of both
arrays:

if (mstr_size > 0)
{
  magic_string_items[num_of_lit] = (jerry_char_t *) (sp_buffer_end_p + 1); /* OOB at num_of_lit == 4096 */
  magic_string_lengths[num_of_lit] = mstr_size;
  num_of_lit++;
}

This is a global out-of-bounds write of an 8-byte pointer plus a
fully-controlled 4-byte value into the adjacent globals. A literals-list with
4097 entries and a one-line script is enough to trigger it:

$ python3 -c "open('lits.list','w').write('1 a\n'*4097)"
$ printf 'var a=1;\n' > src.js
$ jerry-snapshot generate --load-literals-list-format lits.list src.js -o out.snapshot
ERROR: AddressSanitizer: global-buffer-overflow ... WRITE of size 8
    #0 process_generate jerry-main/main-snapshot.c:323
0x... is located 0 bytes after global variable 'magic_string_items'
    defined in 'jerry-main/main-snapshot.c:47' ... of size 32768
SUMMARY: AddressSanitizer: global-buffer-overflow in process_generate

The parser now rejects a list that would exceed the fixed capacity: when
num_of_lit has reached JERRY_LITERAL_LENGTH it logs the error, cleans up and
returns a failure exit code instead of writing past the arrays.

Verification with the documented --jerry-cmdline-snapshot=on build:

• before: SUMMARY: AddressSanitizer: global-buffer-overflow ... in process_generate (exit 1)
• after, 4097 entries: Error: Too many literals in the list (maximum: 4096), no sanitizer report
• after, exactly 4096 entries: Created snapshot file: 'o4096.snapshot' (70 bytes), exit 0

Fixes #5293

JerryScript-DCO-1.0-Signed-off-by: PGZXB pgzxb@qq.com