MDEV-12741: innodb.ibuf_not_empty failed in buildbot with "InnoDB: Trying to do I/O to a tablespace which does not exist"

Background thread is doing ibuf merge, in buf0rea.cc buf_read_ibuf_merge_pages().
It first tries to get page_size and if space is not found it deletes them, but
as we do not hold any mutexes, space can be marked as stopped between that
and buf_read_page_low() for same space. This naturally leads seen error
message on log.

buf_read_page_low(): Add parameter ignore_missing_space = false that
is passed to fil_io()

buf_read_ibuf_merge_pages(): call buf_read_page_low with
ignore_missing_space = true, this function will handle missing
space error code after buf_read_page_low returns.

fil_io(): if ignore_missing_space = true do not print error
message about trying to do I/0 for missing space, just return
correct error code that is handled later.

storage/innobase/buf/buf0rea.cc

@@ -105,6 +105,7 @@ flag is cleared and the x-lock released by an i/o-handler thread.
 @param[in] mode		BUF_READ_IBUF_PAGES_ONLY, ...,
 @param[in] page_id	page id
 @param[in] unzip	true=request uncompressed page
+@param[in] ignore_missing_space  true=ignore missing space when reading
 @return 1 if a read request was queued, 0 if the page already resided
 in buf_pool, or if the page is in the doublewrite buffer blocks in
 which case it is never read into the pool, or if the tablespace does
@@ -118,7 +119,8 @@ buf_read_page_low(
 	ulint			mode,
 	const page_id_t&	page_id,
 	const page_size_t&	page_size,
-	bool			unzip)
+	bool			unzip,
+	bool			ignore_missing_space = false)
 {
 	buf_page_t*	bpage;
 
@@ -178,7 +180,7 @@ buf_read_page_low(
 
 	*err = fil_io(
 		request, sync, page_id, page_size, 0, page_size.physical(),
-		dst, bpage);
+		dst, bpage, ignore_missing_space);
 
 	if (sync) {
 		thd_wait_end(NULL);
@@ -847,7 +849,7 @@ tablespace_deleted:
 				  sync && (i + 1 == n_stored),
 				  0,
 				  BUF_READ_ANY_PAGE, page_id, page_size,
-				  true);
+				  true, true /* ignore_missing_space */);
 
 		switch(err) {
 		case DB_SUCCESS:

storage/innobase/fil/fil0fil.cc

@@ -5158,6 +5158,7 @@ fil_report_invalid_page_access(
 			aligned
 @param[in] message	message for aio handler if non-sync aio
 			used, else ignored
+@param[in] ignore_missing_space true=ignore missing space duging read
 @return DB_SUCCESS, DB_TABLESPACE_DELETED or DB_TABLESPACE_TRUNCATED
 	if we are trying to do i/o on a tablespace which does not exist */
 dberr_t
@@ -5169,7 +5170,8 @@ fil_io(
 	ulint			byte_offset,
 	ulint			len,
 	void*			buf,
-	void*			message)
+	void*			message,
+	bool			ignore_missing_space)
 {
 	os_offset_t		offset;
 	IORequest		req_type(type);
@@ -5248,7 +5250,7 @@ fil_io(
 
 		mutex_exit(&fil_system->mutex);
 
-		if (!req_type.ignore_missing()) {
+		if (!req_type.ignore_missing() && !ignore_missing_space) {
 			ib::error()
 				<< "Trying to do I/O to a tablespace which"
 				" does not exist. I/O type: "

storage/innobase/include/fil0fil.h

@@ -1224,7 +1224,7 @@ fil_space_get_n_reserved_extents(
 				aligned
 @param[in]	message		message for aio handler if non-sync aio
 				used, else ignored
-
+@param[in]	ignore_missing_space true=ignore missing space during read
 @return DB_SUCCESS, DB_TABLESPACE_DELETED or DB_TABLESPACE_TRUNCATED
 if we are trying to do i/o on a tablespace which does not exist */
 dberr_t
@@ -1236,7 +1236,9 @@ fil_io(
 	ulint			byte_offset,
 	ulint			len,
 	void*			buf,
-	void*			message);
+	void*			message,
+	bool			ignore_missing_space = false);
+
 /**********************************************************************//**
 Waits for an aio operation to complete. This function is used to write the
 handler for completed requests. The aio array of pending requests is divided