Allow showing the print preview frame non modally.

Still show the print preview app modally by default, i.e. disabling all the
other windows, but also allow disabling only the preview parent or nothing at
all.

Closes #13108.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67619 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/appbase.cpp

@@ -345,8 +345,11 @@ bool wxAppConsoleBase::Dispatch()
 bool wxAppConsoleBase::Yield(bool onlyIfNeeded)
 {
     wxEventLoopBase * const loop = wxEventLoopBase::GetActive();
+    if ( loop )
+       return loop->Yield(onlyIfNeeded);
 
-    return loop && loop->Yield(onlyIfNeeded);
+    wxScopedPtr<wxEventLoopBase> tmpLoop(CreateMainLoop());
+    return tmpLoop->Yield(onlyIfNeeded);
 }
 
 void wxAppConsoleBase::WakeUpIdle()