PHP Notice in wpmu_validate_blog_signup() when blogname is empty

[DJPaul]

When passing an empty string as $blogname (and $blog_title, for the record) in wpmu_validate_blog_signup(), there is an empty() check, and an error is registered with the WP_Error object.

However, a PHP notice is generated by the nearby "$blogname != $maybe[0]" check. PHP reports that $maybe[0] is undefined.

(This was tested on WP 3.1.1)

[solarissmoke]

Use preg_replace instead of preg_match, avoiding extra variable

[solarissmoke]

Even simpler still

[SergeyBiryukov]

The patch is still good.

[nacin]

In [18524]:

Use preg_match more efficiently. props solarissmoke, fixes #17287.