GC: always look into all keys of the last commit (#9400)

There is a chance that GC might not recognize all live contents, if the commit history is shorter than the cutoff policy _and_(!) commits are not accessible (database corruption).

No realistical functional or behavioral change, rather a precaution.

gc/gc-base/src/main/java/org/projectnessie/gc/identify/IdentifyLiveContents.java

@@ -15,6 +15,8 @@
  */
 package org.projectnessie.gc.identify;
 
+import static java.lang.String.format;
+
 import com.google.common.base.Preconditions;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import jakarta.annotation.Nullable;
@@ -241,6 +243,7 @@ private ReferencesWalkResult identifyContentsForReference(
 
       LogEntryHolder holder = new LogEntryHolder();
       String lastCommitId = null;
+      String finalCommitId = null;
 
       for (Spliterator<LogResponse.LogEntry> spliterator = commits.spliterator();
           spliterator.tryAdvance(holder::set); ) {
@@ -308,33 +311,34 @@ private ReferencesWalkResult identifyContentsForReference(
                           }));
         } else {
           // 1st non-live commit
-          try {
-            numContents += collectAllKeys(addContents, Detached.of(lastCommitId));
-          } catch (NessieNotFoundException e) {
-            throw new RuntimeException(e);
-          }
-          LOGGER.info(
-              "live-set#{}: Finished walking the commit log of {} using {} after {} commits, "
-                  + "commit {} is the first non-live commit.",
-              addContents.id(),
-              namedReference,
-              cutoffPolicy,
-              numCommits,
-              commitHash);
-          return ReferencesWalkResult.single(numCommits, numContents);
+          finalCommitId = commitHash;
+          break;
         }
       }
+
+      // Always consider all content reachable from the last live commit.
+      if (lastCommitId != null) {
+        try {
+          numContents += collectAllKeys(addContents, Detached.of(lastCommitId));
+        } catch (NessieNotFoundException e) {
+          throw new RuntimeException(e);
+        }
+      }
+
+      LOGGER.info(
+          "live-set#{}: Finished walking the commit log of {} using {} after {} commits, {}",
+          addContents.id(),
+          namedReference,
+          cutoffPolicy,
+          numCommits,
+          finalCommitId != null
+              ? format("commit %s is the first non-live commit.", finalCommitId)
+              : "no more commits");
+      return ReferencesWalkResult.single(numCommits, numContents);
     } catch (NessieNotFoundException e) {
       throw new RuntimeException(
           "GC-run#" + addContents.id() + ": Could not find reference " + namedReference, e);
     }
-    LOGGER.info(
-        "live-set#{}: Finished walking the commit log of {} using {} after {} commits, no more commits.",
-        addContents.id(),
-        namedReference,
-        cutoffPolicy,
-        numCommits);
-    return ReferencesWalkResult.single(numCommits, numContents);
   }
 
   @SuppressWarnings("resource")