Fix some errors uncovered via compiler warnings (#7954)

* fix: tray_exist_bits != tray_exist_bits comparison

* fix: title == GetTitle() == title comparison

* fix: possibly dangling reference to a temporary
```
OrcaSlicer/src/libslic3r/calib.cpp:456:17: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  456 |     const auto &w         = bed_ext.size().x();
OrcaSlicer/src/libslic3r/calib.cpp:456:45: note: the temporary was destroyed at the end of the full expression ‘((Eigen::DenseCoeffsBase<Eigen::Matrix<double, 2, 1, 2>, 1>*)(& Slic3r::BoundingBoxBase<PointClass>::size() const [with PointClass = Eigen::Matrix<double, 2, 1, 2>]()))->Eigen::DenseCoeffsBase<Eigen::Matrix<double, 2, 1, 2>, 1>::x()’
  456 |     const auto &w         = bed_ext.size().x();
```

* fix: mixup of | and ||
in this case I think it actually does not change the semantics it just means that both comparison have to be evaluated.

* fix: multi-character character constants need "

OrcaSlicer/src/slic3r/GUI/MediaPlayCtrl.cpp:392: warning: multi-character character constant [-Wmultichar]
  392 |     if (auto n = tunnel.find_first_of('/_'); n != std::string::npos)
OrcaSlicer/src/slic3r/GUI/MediaPlayCtrl.cpp: In member function ‘void Slic3r::GUI::MediaPlayCtrl::Stop(const wxString&)’:
OrcaSlicer/src/slic3r/GUI/MediaPlayCtrl.cpp:392: warning: overflow in conversion from ‘int’ to ‘char’ changes value from ‘12127’ to ‘95’ [-Woverflow]

* fix: missing paranthesis - skips null check

* NFC: Remove this check it can never be false

* NFC: fix warning: statement has no effect

src/slic3r/GUI/MainFrame.cpp

@@ -916,7 +916,6 @@ void MainFrame::update_title_colour_after_set_title()
 
 void MainFrame::show_option(bool show)
 {
-    if (!this) { return; }
     if (!show) {
         if (m_slice_btn->IsShown()) {
             m_slice_btn->Hide();