Additional fix for 18201 XML: ExtractValue works even if the xml fragment is not well-formed xml

extractValue('<a>a','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 5: unexpected END-OF-INPUT'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 5: unexpected END-OF-INPUT'

select extractValue('<a>a<','/a');

extractValue('<a>a<','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 6: END-OF-INPUT unexpected (ident or '/' wanted)'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 6: END-OF-INPUT unexpected (ident or '/' wanted)'

select extractValue('<a>a</','/a');

extractValue('<a>a</','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 7: END-OF-INPUT unexpected (ident wanted)'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 7: END-OF-INPUT unexpected (ident wanted)'

select extractValue('<a>a</a','/a');

extractValue('<a>a</a','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 8: END-OF-INPUT unexpected ('>' wanted)'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 8: END-OF-INPUT unexpected ('>' wanted)'

select extractValue('<a>a</a></b>','/a');

extractValue('<a>a</a></b>','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 12: '</b>' unexpected (END-OF-INPUT wanted)'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 12: '</b>' unexpected (END-OF-INPUT wanted)'

select extractValue('<a b=>a</a>','/a');

extractValue('<a b=>a</a>','/a')

NULL

Warnings:

Warning	1504	Incorrect XML value: 'parse error at line 1 pos 7: '>' unexpected (ident or string wanted)'

Warning	1512	Incorrect XML value: 'parse error at line 1 pos 7: '>' unexpected (ident or string wanted)'

select extractValue('<e>1</e>','position()');

ERROR HY000: XPATH syntax error: ''

select extractValue('<e>1</e>','last()');