Don't attempt to verify checksums on new pages

Teach both base backups and pg_verify_checksums that if a page is new,
it does not have a checksum yet, so it shouldn't be verified.

Noted by Tomas Vondra, review by David Steele.

src/backend/replication/basebackup.c

@@ -1446,8 +1446,10 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
 				 * written only halfway and the checksum would not be valid.
 				 * However, replaying WAL would reinstate the correct page in
 				 * this case.
+				 * We also skip completely new pages, since they don't have
+				 * a checksum yet.
 				 */
-				if (PageGetLSN(page) < startptr)
+				if (!PageIsNew(page) && PageGetLSN(page) < startptr)
 				{
 					checksum = pg_checksum_page((char *) page, blkno + segmentno * RELSEG_SIZE);
 					phdr = (PageHeader) page;

src/bin/pg_verify_checksums/pg_verify_checksums.c

@@ -106,6 +106,10 @@ scan_file(char *fn, int segmentno)
 		}
 		blocks++;
 
+		/* New pages have no checksum yet */
+		if (PageIsNew(buf))
+			continue;
+
 		csum = pg_checksum_page(buf, blockno + segmentno * RELSEG_SIZE);
 		if (csum != header->pd_checksum)
 		{