Fix paragraph position in TextMetrics::singleParUpdate()

Fix paragraph position in TextMetrics::singleParUpdate()

When running redoParagraph, it may happen that the ascent of the first
row changes. Since the ParagraphMetrics position is actually the
baseline of its first row, it may be necessary to update it.

Fixes bug #11601.

(cherry picked from commit 2e8c9cfc832d876ff66e47ae7aadc30fe9328e9d)