Fix argument given to buffer_readv_encode_error()

buffer_readv_encode_error() expects a uint8 for its "error_count"
argument, but the value given was a boolean.  That's harmless in
practice, but let's be clean.

Thinko in 047cba7fa0.

Author: Antonin Houska <ah@cybertec.at>
Reviewed-by: Steven Niu <niushiji@gmail.com>
Discussion: https://postgr.es/m/8073.1791959482@localhost
Backpatch-through: 18

src/backend/storage/buffer/bufmgr.c

@@ -8690,7 +8690,7 @@ buffer_readv_complete_one(PgAioTargetData *td, uint8 buf_off, Buffer buffer,
 			buffer_readv_encode_error(&result_one, is_temp,
 									  *zeroed_buffer,
 									  *ignored_checksum,
-									  *buffer_invalid,
+									  *buffer_invalid ? 1 : 0,
 									  *zeroed_buffer ? 1 : 0,
 									  *failed_checksum ? 1 : 0,
 									  buf_off, buf_off, buf_off);