add logging message when an invalid file ending is encountered

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

@@ -164,6 +164,9 @@ public class CityDoctorValidation {
 			startFileValidation(inputFile, xmlOutput, pdfOutput, config, outputFile);
 		} else if (inputFile.getName().endsWith(".zip")) {
 			startZipValidation(input, xmlOutput, pdfOutput, config, outputFile);
+		} else {
+			logger.error("Input file '{}' does not end with .gml or .xml and is not a zip archive.", input);
+			System.exit(1);
 		}
 	}
 

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

 package de.hft.stuttgart.citydoctor2;
 
-import picocli.CommandLine;
+import java.util.concurrent.Callable;
+
 import picocli.CommandLine.Command;
 import picocli.CommandLine.Option;
-import picocli.CommandLine.Parameters;
-
-import java.util.concurrent.Callable;
 
 @Command(name =  "citydoctor2", mixinStandardHelpOptions = true, description = "Validates CityGML files according to a provided validation-plan.")
 public class CityDoctorValidationCLI implements Callable<Integer> {