amcheck: Fix incorrect use of VARATT_IS_COMPRESSED.

The macro is being applied to a TOAST pointer, not a varlena header.
Therefore the use of VARATT_IS_COMPRESSED() is wrong. We can check
VARATT_EXTERNAL_IS_COMPRESSED(), but then we don't need the length
check that follows.

Report and fix by Kyotaro Horiguchi.

Discussion: http://postgr.es/m/20220517.162719.1671558681467343711.horikyota.ntt@gmail.com

Author: robertmhaas

contrib/amcheck/verify_heapam.c

@@ -1385,19 +1385,11 @@ check_tuple_attribute(HeapCheckContext *ctx)
 								   toast_pointer.va_rawsize,
 								   VARLENA_SIZE_LIMIT));
 
-	if (VARATT_IS_COMPRESSED(&toast_pointer))
+	if (VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
 	{
 		ToastCompressionId cmid;
 		bool		valid = false;
 
-		/* Compression should never expand the attribute */
-		if (VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer) > toast_pointer.va_rawsize - VARHDRSZ)
-			report_corruption(ctx,
-							  psprintf("toast value %u external size %u exceeds maximum expected for rawsize %d",
-									   toast_pointer.va_valueid,
-									   VARATT_EXTERNAL_GET_EXTSIZE(toast_pointer),
-									   toast_pointer.va_rawsize));
-
 		/* Compressed attributes should have a valid compression method */
 		cmid = TOAST_COMPRESS_METHOD(&toast_pointer);
 		switch (cmid)