git-gui: Correct stock message for 'Invalid font specified in %s'

This particular message is talking about a specific option in the
configuration file named "gui.$name".  This option is not localized
so we cannot localize the "gui." that denotes the section the option
$name is found within.  Currently there are no plans to localize the
configuration options for git-gui, but if that were to change in the
future then it would be necessary to localize not only the "gui."
section prefix but also the $name (fontui and fontdiff).

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1643,7 +1643,7 @@ proc apply_config {} {
 				font configure $font $cn $cv
 			}
 			} err]} {
-			error_popup [append [mc "Invalid font specified in gui.%s:" $name] "\n\n$err"]
+			error_popup [append [mc "Invalid font specified in %s:" "gui.$name"] "\n\n$err"]
 		}
 		foreach {cn cv} [font configure $font] {
 			font configure ${font}bold $cn $cv