Fix escaped backslash at end of string literal preventing string closure

[callumwalker]

If a string literal ended with an escaped backslash that was being interpreted as an escaped quote preventing the string from ending. If the next string contained a ? or %s that was then treated as a parameter and a traceback was raised as the number of parameters in the statement didn't match the number supplied.

import mariadb

conn = mariadb.connect(user='root', database='db')
cursor = conn.cursor()

cursor.execute(r"INSERT INTO result VALUES (1, '\\', '?')")

Traceback (most recent call last):
  File "sql.py", line 6, in <module>
    cursor.execute(r"INSERT INTO result VALUES (1, '\\', '?')")
  File ".venv/lib64/python3.12/site-packages/mariadb/cursors.py", line 318, in execute
    self._parse_execute(statement, (data))
  File ".venv/lib64/python3.12/site-packages/mariadb/cursors.py", line 258, in _parse_execute
    self._check_execute_params()
  File ".venv/lib64/python3.12/site-packages/mariadb/cursors.py", line 195, in _check_execute_params
    raise mariadb.ProgrammingError(
mariadb.ProgrammingError: statement (1) doesn't match the number of data elements (0).