Don't assert if starting search position in LVN_ODFINDITEM is invalid.

Don't assert if starting search position in LVN_ODFINDITEM is invalid.

Just use wxLogDebug() if this happens, asserting here is not the right thing
to do as it doesn't indicate an error in the program but rather invalid
external input and, moreover, we can recover from it easily.

No changes in behaviour in normal case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67154 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775