Set continuous version to invalidVersion when snapshot version is the target version

fdbclient/BackupContainer.actor.cpp

@@ -1353,6 +1353,7 @@ public:
 			// No logs needed if there is a complete key space snapshot at the target version.
 			if (snapshot.get().beginVersion == snapshot.get().endVersion &&
 			    snapshot.get().endVersion == targetVersion) {
+				restorable.continuousBeginVersion = restorable.continuousEndVersion = invalidVersion;
 				return Optional<RestorableFileSet>(restorable);
 			}
 

fdbclient/BackupContainer.h

@@ -197,7 +197,8 @@ struct RestorableFileSet {
 	// Range file's key ranges. Can be empty for backups generated before 6.3.
 	std::map<std::string, KeyRange> keyRanges;
 
-	// Mutation logs continuous range [begin, end)
+	// Mutation logs continuous range [begin, end). Both can be invalidVersion
+	// when the entire key space snapshot is at the target version.
 	Version continuousBeginVersion, continuousEndVersion;
 
 	KeyspaceSnapshotFile snapshot; // Info. for debug purposes