LibPartition: Fix end block off by one error

Previously, end block was inconsistent. GUIDPartitionTable treated
end block as an inclusive bound, while MBRPartitionTable and
EBRPartitionTable treated end block as an exclusive bound.
Now all three treat end block as an inclusive upper bound.

Userland/Libraries/LibPartition/EBRPartitionTable.cpp

@@ -77,7 +77,7 @@ EBRPartitionTable::EBRPartitionTable(NonnullRefPtr<Core::File> device)
         if (entry.offset == 0x00) {
             continue;
         }
-        MUST(m_partitions.try_empend(entry.offset, (entry.offset + entry.length), entry.type));
+        MUST(m_partitions.try_empend(entry.offset, (entry.offset + entry.length) - 1, entry.type));
     }
 }