core: back-up to kvdb for a pruned block

core/rawdb/accessors_chain.go

@@ -440,6 +440,12 @@ func ReadBodyRLP(db ethdb.Reader, hash common.Hash, number uint64) rlp.RawValue
 		// Check if the data is in ancients
 		if isCanon(reader, number, hash) {
 			data, _ = reader.Ancient(ChainFreezerBodiesTable, number)
+			// The freezer might be pruned. In the particular case of genesis, the block
+			// will be still available in kvdb. The full genesis block is needed on startup
+			// sometimes for repair.
+			if data == nil {
+				data, _ = db.Get(blockBodyKey(number, hash))
+			}
 			return nil
 		}
 		// If not, try reading from leveldb