Fixes an error with query parameters in the LoginFilter

The redirect created in the LoginFilter when the request URL included
query parameters was incomplete, as it missed the "?" that separates the
query parameters from the request URL. This commit fixes this error.

src/main/java/es/uvigo/esei/daa/LoginFilter.java

@@ -101,7 +101,7 @@ public class LoginFilter implements Filter {
 	) throws IOException {
 		String redirectPath = request.getRequestURI();
 		if (request.getQueryString() != null)
-			redirectPath += request.getQueryString();
+			redirectPath += "?" + request.getQueryString();
 		
 		response.sendRedirect(redirectPath);
 	}