screenshare: round captureBox after scaling to fix region capture at fractional scales (#14257)

After scaling m_captureBox from logical to pixel coordinates, the box may
have non-integer dimensions (e.g. logical 401x301 at scale 1.25 -> pixel
501.25x376.25). m_bufferSize is then computed as captureBox.size() and
sent to the client as int32 width/height (truncating the fraction), but
m_bufferSize itself stays as a fractional Vector2D.

When the client allocates the integer-sized buffer and submits it,
CScreenshareFrame::share() rejects it with ERROR_BUFFER_SIZE because
Vector2D::operator== is exact double comparison: (501, 376) != (501.25,
376.25). The frame is sent failed, and the client retries forever.

The SHARE_WINDOW path already rounds its bufferSize; the SHARE_REGION
path didn't. Round the captureBox immediately after scaling so all
downstream consumers (m_bufferSize, render translates) see clean integer
pixel coordinates.

Reproducer at scale 1.25 on a 1920x1080 monitor:

  wf-recorder -g '500,200 401x301' -f /tmp/x.mp4
  # "Failed to copy frame, retrying..." until exit

  wf-recorder -g '500,200 400x300' -f /tmp/x.mp4
  # works (400*1.25=500, 300*1.25=375, both integer)

0 files changed, 0 insertions, 0 deletions