A memory region starts from REGION_START and ends at
(REGION_START+SIZE-1).
Prior to this change, the check assumes a to-be-added region starting from REGION_START is invalid. Let's take an easy example:
A memory region: 0x1000~0x10ff
new added region: 0x1000~0x1020
This will be valid.
Valid conditions and invalid conditions are illustrated in the code comment