Post content didn't import properly due to parsing issue in get_tag

[vabc3]

Exported XML via wordpress 5.1 could not be properly imported.

The imported content will always have ]> at end of post.

The xml is like:

<content:encoded>
\t\t<![CDATA[some stuff]]>
\t\t</content:encoded>

This is valid XML, but it will cause issue in current parsing logic:

wordpress-importer/src/parsers/class-wxr-parser-regex.php

Lines 115 to 118 in 64e575a

	function get_tag( $string, $tag ) {
	preg_match( "|<$tag.*?>(.*?)</$tag>|is", $string, $return );
	if ( isset( $return[1] ) ) {
	if ( substr( $return[1], 0, 9 ) == '<![CDATA[' ) {

'<![CDATA[' is not the heading content, here we need to 'trim' content inside the tag first.

A quick fix is to add \s* around (.*?) in preg_match.