MDEV-10970: Crash while loading mysqldump backup when InnoDB encryption is enabled

Follow-up: Make sure we do not reference NULL-pointer when space is being
dropped and does not contain any nodes.

storage/innobase/fil/fil0fil.cc

@@ -1001,8 +1001,13 @@ fil_mutex_enter_and_prepare_for_io(
 	does not exist, we handle the situation in the function which called
 	this function */
 
-	if (!space || UT_LIST_GET_FIRST(space->chain)->open) {
+	if (!space) {
+		return;
+	}
+
+	fil_node_t*	node = UT_LIST_GET_FIRST(space->chain);
 
+	if (!node || node->open) {
 		return;
 	}
 

storage/xtradb/fil/fil0fil.cc

@@ -1002,8 +1002,13 @@ fil_mutex_enter_and_prepare_for_io(
 	/* If the file is already open, no need to do anything; if the space
 	does not exist, we handle the situation in the function which called
 	this function */
+	if (!space) {
+		return;
+	}
+
+	fil_node_t*	node = UT_LIST_GET_FIRST(space->chain);
 
-	if (!space || UT_LIST_GET_FIRST(space->chain)->open) {
+	if (!node || node->open) {
 
 		return;
 	}