row_search_mvcc(): Revise an overflow check, disabling it on 64-bit
systems. The maximum number of consecutive record reads in a key range
scan should be limited by the maximum number of records per page
(less than 2^13) and the maximum number of pages per tablespace (2^32)
to less than 2^45. On 32-bit systems we can simplify the overflow check.

Reviewed by: Vladislav Lesin