branches/5.1: In os_mem_alloc_large(), if we fail to attach

the shared memory, reset memory pointer ptr to NULL, and
allocate memory from conventional pool. This is a port
from branches/zip.
Bug #48237 Error handling in os_mem_alloc_large appears to be incorrect
rb://198  Approved by: Marko

os/os0proc.c

@@ -591,6 +591,7 @@ os_mem_alloc_large(
 			fprintf(stderr, "InnoDB: HugeTLB: Warning: Failed to"
 				" attach shared memory segment, errno %d\n",
 				errno);
+			ptr = NULL;
 		}
 
 		/* Remove the shared memory segment so that it will be