fix wrong part_size calculation (1 sector missing)

[steadfasterX]

IRC excerpt: [12-20 15:20] i have a partition: end=378879 start=377856 [12-20 15:21] so the calcluation would be 378879-377856 [12-20 15:21] which is 1023 [12-20 15:21] which can never be correct [12-20 15:22] this is bc in the calculation it will need to include the start (or end) sector itself [12-20 15:23] when i dump without that +1 i miss exact 512 bytes so 1 sector

[steadfasterX]

Well that's how I implemented it the first time but others suggested to do it that way as it aims to be more logical but well.. Should I change it?

[Lekensteyn]

Ah too much effort for such a detail, I'll merge it. Thanks!