Demote "skipping textdomain" error to warning level

The "no location found for '<path>', skipping textdomain" error message
is usually inoffensive and merely means that there is a textdomain
declaration pointing to a directory that doesn't exist, so it shouldn't
really be an error. Since we don't have anything midway between warning
and info messages, this should remain in place as a warning for WML
coders typoing textdomain declarations or forgetting to include their
add-on's translations with it.

src/language.cpp

@@ -305,7 +305,7 @@ void init_textdomains(const config& cfg)
 			if (location.empty()) {
 				//if location is empty, this causes a crash on Windows, so we
 				//disallow adding empty domains
-				ERR_G << "no location found for '" << path << "', skipping textdomain" << std::endl;
+				WRN_G << "no location found for '" << path << "', skipping textdomain" << std::endl;
 			} else {
 				t_string::add_textdomain(name, location);
 			}