Fix broken image path

Someone typoed a line, resulting in the image path
"units/human-outlaws/rogue+female-attack:250.png" instead of
"units/human-outlaws/rogue+female-attack.png:250".

This fixes a warning and missing animation frame when female Rouges play
their ranged attack animation:

> error display: could not open image 'units/human-outlaws/rogue+female-attack'

git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56494 75b3775d-3801-0410-9e12-e2e43121521d