WXR import error when no tags are used

[fitztrev]

When importing a WP Export file, the following error occurs:

Warning: array_shift() [function.array-shift]: The argument should be an array in /home/fitztrev/public_html/trunk/wp-admin/import/wordpress.php on line 238

This was tested between 2 trunk installations, both revision 6381.

[fitztrev]

This occurs because the 'tags' variable is only casted into an array once a tag has been found. If the blog owner has never used tags before, this causes a problem. This patch initializes the 'tags' variable as an array at the beginning of the import class.

To recreate:

1) Have 2 fresh installations side by side.

2) Export content from 1 WP instance from Manage>Export

3) Import that file on the second WP instance from Manage>Import>WordPress

*) Then try again, but give Hello World a tag.

[ryan]

(In [6565]) Init tags array. Props fitzrev. fixes #5468