When space cost factor is large, wass may run into a problem caused by the limited precision of floating point arithmetic. When that happens the code reaches a statement that was thought to be unreachable.

This patch adds a check that detects the situation and generates
a more suitable error message.

Target: trunk
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: yes
Require-book: no
Acked-by: Karsten Schwank <karsten.schwank@desy.de>
Patch: https://rb.dcache.org/r/7399