Refactor: Reduce hard drive usage for getFileSize()

Use a BufferedInputStream for counting the bytes of a ZipEntry to reduce
the number of read operations on the hard drive.

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipEntryFile.java

 package de.hft.stuttgart.citydoctor2.zip;
 
+import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.zip.ZipEntry;
@@ -33,7 +34,7 @@ public class CityGmlZipEntryFile implements AutoCloseable {
         if (cgmlZipEntry.getFileSize() == -1L) {
             if (zipEntry.getSize() == -1) {
                 long bytes = 0;
-                InputStream is = this.getInputStream();
+                InputStream is = new BufferedInputStream(this.getInputStream());
                 for (int i = is.read(); i != -1; i = is.read()) {
                     bytes++;
                 }