Fix 37 pixels offset for the context menu when dropping.

Bug found by tsdgeos.
Regression coming from the fix for bug 430787.
2 jobs for !48 with work/dfaure/fix_contextmenu_pos in 44 minutes and 23 seconds (queued for 105 minutes and 1 second)
latest detached
Status Job ID Name Coverage
  Build
passed #92184
build_clazy_clang_tidy

00:31:21

passed #92183
linux kf5-qt5 qt5.15

00:13:02

1.0%