Avoids allocating a QString for every char being written out.
The benchmark went from 5.5 ms per iteration to 0.8 ms,
and from 40 million instructions to 6 million.
Found using Milian Wolff's heaptrack tool.
Change-Id: I1784c47b944454bc947a607a22c39d249372ed55
Reviewed-by: Adam Majer <adamm@zombino.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
