Thickbox images can't be loaded in network admin

[ocean90]

The reason is:

if ( typeof tb_pathToImage != 'string' ) {
	var tb_pathToImage = "../wp-includes/js/thickbox/loadingAnimation.gif";
}
if ( typeof tb_closeImage != 'string' ) {
	var tb_closeImage = "../wp-includes/js/thickbox/tb-close.png";
}

Image link for network admin => wp.local/wp-admin/wp-includes/js/thickbox/tb-close.png

See also #6453.

[nacin]

Where are we using thickbox in the network admin?

If we are, then we should define those variables and inject them into the head when we need it. (That's the purpose of the check, which was added by us into TB.)

[ocean90]

Theme preview or plugin (upgrade) infos are usin thickbox.

[nacin]

Can the add_action() be put directly into add_thickbox if is_network_admin()? Seems cleaner.

[ocean90]

Replying to nacin:

Can the add_action() be put directly into add_thickbox if is_network_admin()? Seems cleaner.

Sure, why not. Patch attached.

[nacin]

(In [16963]) Plugin install and thickbox for the network admin. props ocean90, fixes #15510, fixes #15750.