Merge branch 'stable-5.1' into stable-5.2

* stable-5.1:
  Prepare 5.1.16-SNAPSHOT builds
  JGit v5.1.15.202012011955-r
  Fix PackInvalidException when fetch and repack run concurrently

Change-Id: Id83e29e567646a3945a5b817860ea8f7c3e6e5cf
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackFile.java

@@ -684,6 +684,7 @@ public class PackFile implements Iterable<PackIndex.MutableEntry> {
 
 	private void doOpen() throws IOException {
 		if (invalid) {
+			openFail(true, invalidatingCause);
 			throw new PackInvalidException(packFile, invalidatingCause);
 		}
 		try {