Correct some code in pg_restore when reading the header of a tar archive:

(1) The code doesn't initialize `sum', so the initial "does the checksum
    match?" test is wrong.

(2) The loop that is intended to check for a "null block" just checks
    the first byte of the tar block 512 times, rather than each of the
    512 bytes one time (!), which I'm guessing was the intent.

It was only through sheer luck that this worked in the first place.

Per Coverity static analysis performed by EnterpriseDB.

src/bin/pg_dump/pg_backup_tar.c

@@ -16,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *		$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_tar.c,v 1.47 2005/01/25 22:44:31 tgl Exp $
+ *		$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_tar.c,v 1.48 2005/06/22 02:00:47 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1155,7 +1155,6 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
 	size_t		len;
 	unsigned long ullen;
 	off_t		hPos;
-	int			i;
 	bool		gotBlock = false;
 
 	while (!gotBlock)
@@ -1178,7 +1177,7 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
 		hPos = ctx->tarFHpos;
 
 		/* Read a 512 byte block, return EOF, exit if short */
-		len = _tarReadRaw(AH, &h[0], 512, NULL, ctx->tarFH);
+		len = _tarReadRaw(AH, h, 512, NULL, ctx->tarFH);
 		if (len == 0)			/* EOF */
 			return 0;
 
@@ -1188,20 +1187,22 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
 						 (unsigned long) len);
 
 		/* Calc checksum */
-		chk = _tarChecksum(&h[0]);
+		chk = _tarChecksum(h);
+		sscanf(&h[148], "%8o", &sum);
 
 		/*
-		 * If the checksum failed, see if it is a null block. If so, then
-		 * just try with next block...
+		 * If the checksum failed, see if it is a null block. If so,
+		 * silently continue to the next block.
 		 */
-
 		if (chk == sum)
 			gotBlock = true;
 		else
 		{
+			int			i;
+
 			for (i = 0; i < 512; i++)
 			{
-				if (h[0] != 0)
+				if (h[i] != 0)
 				{
 					gotBlock = true;
 					break;
@@ -1213,7 +1214,6 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
 	sscanf(&h[0], "%99s", tag);
 	sscanf(&h[124], "%12lo", &ullen);
 	len = (size_t) ullen;
-	sscanf(&h[148], "%8o", &sum);
 
 	{
 		char		buf[100];