Unsafe escaping in enquoteLiteral()/enquoteNCharLiteral()

SQL injection in new JDBC 4.3 enquoteLiteral() and enquoteNCharLiteral()

Both methods fail to safely quote values, allowing input to break out of the literal:

enquoteLiteral emits ' as \' (via Matcher.appendReplacement, which collapses the doubled backslash). Under NO_BACKSLASH_ESCAPES the backslash isn't an escape, so the quote closes the string early.
Backslashes are left undoubled, so a trailing \ escapes the closing quote under the default sql_mode. enquoteNCharLiteral never escapes backslashes at all.

Repro:

Driver.enquoteLiteral("x' OR '1'='1");  // → 'x\' OR \'1\'=\'1'  (injection under NO_BACKSLASH_ESCAPES)

Driver.enquoteLiteral("a\\");           // → 'a\'  (literal stays open under default mode)

thanks jmestwa-coder for PR https://github.com/mariadb-corporation/mariadb-connector-j/pull/228/changes