statistics: don't place labels at half-integer values

Placing labels at half-integer values gives horrible
rendering artifacts. Therefore, always round to integer
values. The easiest way to do this is right before setting
the position. Introduce a helper function to round QPointF
in such scenarios.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

stats/statshelper.cpp

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "statshelper.h"
+
+#include <cmath>
+
+QPointF roundPos(const QPointF &p)
+{
+	return QPointF(round(p.x()), round(p.y()));
+}