FilterCommandsTest fails on Windows

Bug: 538068
Change-Id: I3ba6fceef2c34cacc0c37150206379aa93b5e3d0
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FilterCommandsTest.java

@@ -85,6 +85,8 @@ public class FilterCommandsTest extends RepositoryTestCase {
 				public int run() throws IOException {
 					int b = in.read();
 					if (b == -1) {
+						in.close();
+						out.close();
 						return b;
 					}
 					out.write(prefix);