[FIX] base: no-break hyphen

- Create an invoice with two products
- Each line has a long description (spread on 2 lines)
- The second line has a negative value
- Print the invoice (PDF)

The amount spreads on two lines, split as:
$ -
1,000.00

This is due to the wkhtmltopdf version with patched QT. Unfortunately,
upgrading to the latest version 0.12.4 doesn't solve the problem.

The solution is to replace the '-' by a non-breakable hyphen.

opw-711002