Fix bug #8238: correct the forward argument of replace2string() in on_replacePB_click...

Fix bug #8238: correct the forward argument of replace2string() in on_replacePB_clicked().
(cherry picked from commit 44b327800666f30d2713c6c9e26f275aadfa4b9c)
Fix the wrong cursor move when forward flag is false:
The forward flag is used to place the cursor behind the replaced text if it's true.
But it's not correct to move the cursor if it's false. The cursor is in front of the
replacement already after the replaceSelectionWithString() was done.
(cherry picked from commit 430cf3ee5ef125b8bc610300afca58437b734306)