get_avatar produces invalid XHTML for default avatar

[Otto42]

Trunk. pluggable.php, line 1253 or thereabouts.

$avatar = "<img alt='' src='{$default}' class='avatar avatar-{$size} avatar-default' height='{$size}' width='{$size}'>";

That's an unclosed image tag. It should be:

$avatar = "<img alt='' src='{$default}' class='avatar avatar-{$size} avatar-default' height='{$size}' width='{$size}' />";

Tagging this as high/major because it makes default out-of-the-box installs fail validation. Also, it's a 2 character fix.

(In [7461]) Close img tag. Props Otto42. fixes #6339