reenable validation of xml files

CityDoctorParent/CityDoctorValidation/src/main/java/de/hft/stuttgart/citydoctor2/CityDoctorValidation.java

@@ -160,7 +160,7 @@ public class CityDoctorValidation {
 			logger.error("Input file '{}' does not exist.", input);
 			System.exit(1);
 		}
-		if (inputFile.getName().endsWith(".gml")) {
+		if (inputFile.getName().endsWith(".gml") || inputFile.getName().endsWith(".xml")) {
 			startFileValidation(inputFile, xmlOutput, pdfOutput, config, outputFile);
 		} else if (inputFile.getName().endsWith(".zip")) {
 			startZipValidation(input, xmlOutput, pdfOutput, config, outputFile);