Fix the new ARMv8 CRC code for short and unaligned input.

The code before the main loop, to handle the possible 1-7 unaligned bytes
at the beginning of the input, was broken, and read past the input, if the
the input was very short.

src/port/pg_crc32c_armv8.c

@@ -29,17 +29,17 @@ pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t len)
 	 * significantly faster. Process leading bytes so that the loop below
 	 * starts with a pointer aligned to eight bytes.
 	 */
-	if (!PointerIsAligned(p, uint16) && p < pend)
+	if (!PointerIsAligned(p, uint16) && p + 1 <= pend)
 	{
 		crc = __crc32cb(crc, *p);
 		p += 1;
 	}
-	if (!PointerIsAligned(p, uint32) && p < pend)
+	if (!PointerIsAligned(p, uint32) && p + 2 <= pend)
 	{
 		crc = __crc32ch(crc, *(uint16 *) p);
 		p += 2;
 	}
-	if (!PointerIsAligned(p, uint64) && p < pend)
+	if (!PointerIsAligned(p, uint64) && p + 4 <= pend)
 	{
 		crc = __crc32cw(crc, *(uint32 *) p);
 		p += 4;