fdo#37584: Make a real copy of the text where to count words
fdo#37584: Make a real copy of the text where to count words

Const-casting a reference doesn't create a copy of it and then the
spaces replacement made by the WordCount was also made on the actual
text node. Use String::Copy() to actually copy the text and safely
operate on it.

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core