PG-1605 Fix encryption with old keys with disabled WAL encryption

To not break recovery when we replay encrypted WAL but WAL encryption is
disabled the simplest way is to treat disabled WAL encryption just like
enabled WAL encryption. The issue is not big in practice since it should
only hit users who disable WAL encryption and then crash the database
but treating both cases the same way makes the code simple to
understand.

contrib/pg_tde/src/access/pg_tde_xlog_smgr.c

@@ -23,7 +23,6 @@
 #ifdef FRONTEND
 #include "pg_tde_fe.h"
 #else
-#include "pg_tde_guc.h"
 #include "port/atomics.h"
 #endif
 
@@ -138,11 +137,8 @@ TDEXLogEncryptStateSize(void)
 	Size		sz;
 
 	sz = sizeof(EncryptionStateData);
-	if (EncryptXLog)
-	{
 	sz = add_size(sz, TDEXLogEncryptBuffSize());
 	sz = add_size(sz, PG_IO_ALIGN_SIZE);
-	}
 
 	return sz;
 }
@@ -169,12 +165,9 @@ TDEXLogShmemInit(void)
 
 	memset(EncryptionState, 0, sizeof(EncryptionStateData));
 
-	if (EncryptXLog)
-	{
 	EncryptionBuf = (char *) TYPEALIGN(PG_IO_ALIGN_SIZE, ((char *) EncryptionState) + sizeof(EncryptionStateData));
 
 	Assert((char *) EncryptionState + TDEXLogEncryptStateSize() >= (char *) EncryptionBuf + TDEXLogEncryptBuffSize());
-	}
 
 	pg_atomic_init_u64(&EncryptionState->enc_key_lsn, 0);
 
@@ -367,12 +360,8 @@ tdeheap_xlog_seg_write(int fd, const void *buf, size_t count, off_t offset,
 	{
 		WALKeyCacheRec *last_key = pg_tde_get_last_wal_key();
 
-		if (!crashRecovery || EncryptionKey.type == WAL_KEY_TYPE_UNENCRYPTED)
+		if (!crashRecovery)
 		{
-			/*
-			 * TODO: the unencrypted case is still not perfect, we need to
-			 * report an error in some cornercases
-			 */
 			if (last_key == NULL || last_key->start.lsn < loc.lsn)
 			{
 				pg_tde_wal_last_key_set_location(loc);
@@ -383,7 +372,7 @@ tdeheap_xlog_seg_write(int fd, const void *buf, size_t count, off_t offset,
 		}
 	}
 
-	if ((!afterWriteKey || !lastKeyUsable) && EncryptionKey.type == WAL_KEY_TYPE_ENCRYPTED)
+	if ((!afterWriteKey || !lastKeyUsable) && EncryptionKey.type != WAL_KEY_TYPE_INVALID)
 	{
 		return TDEXLogWriteEncryptedPagesOldKeys(fd, buf, count, offset, tli, segno, segSize);
 	}