RVE DB reader does not read 64bit coordinates even if built with 64bit option

This ticket refers to this forum entry: https://www.klayout.de/forum/discussion/1524/unable-to-open-high-value-rve-file-from-high-precision-db-drc#latest

The fix can be applied also for the case of non-64bit-coordinates builds as RVE objects store their coordinates in floating-point values.