Crash on cutting on Windows

[Vincent van Ravesteijn]

Commit db358a (Richard Heck; Fix bug found by Scott concerning copying 
XHTML to clipboard) introduces a bug that crashes LyX when something is 
cut the second time.

Since commit 928dc0332 (Georg Baum; Fic crash for repeated pasting from 
complex docs) LyX crashes immediately on every cut.

Vincent