Tag not closed in theme editor when the file does not have a description

[roganty]

I've noticed this before problem before, but I didn't think anything of it.

The problem is to do when the file being edited doesn't have a description, the strong tag is not closed in the title.

There are two ways this could be fixed, but they both give different results.

The first way is to add the opening strong tag to the start of the variable $desc_header and to remove the opening strong tag from where the variable is printed to the screen.
If there is no description this fix will not make the file name bold.

The second way is to add the closing strong tag to the end of the variable $desc_header
If there is no description this fix will make the file name bold.

[roganty]

Closes tag and removes formatting from file name with no description

[roganty]

Closes tag and keeps formatting for file name with no description

[azaozz]

(In [10194]) Fix missing closing tag in theme-editor.php, props roganty, fixes #8581

[ryan]

(In [10195]) Fix missing closing tag in theme-editor.php, props roganty, fixes #8581 for 2.7