Fix typo in the CodeBlocks project file

Apparently CB can't deal with invalid XML properly. The result was that
every file listed after that point wasn't being compiled or passed to the
linker, resulting in a flood of linker errors.

projectfiles/CodeBlocks/wesnoth.cbp

@@ -1056,7 +1056,7 @@
 		<Unit filename="..\..\src\unit_types.hpp" />
 		<Unit filename="..\..\src\util.cpp" />
 		<Unit filename="..\..\src\util.hpp" />
-		<Unit filename="..\..\src\utils\boost_function_guarded.hpp">
+		<Unit filename="..\..\src\utils\boost_function_guarded.hpp" />
 		<Unit filename="..\..\src\utils\iterator.hpp" />
 		<Unit filename="..\..\src\utils\reference_counter.hpp" />
 		<Unit filename="..\..\src\utils\sha1.cpp" />