Return -1 from GetLineLength() if line number is out of range

Make wxTextCtrl behaviour in all ports consistent with the documentation
and also update wxStyledTextCtrl to behave accordingly.

Closes #18431.

src/univ/textctrl.cpp

@@ -1684,8 +1684,8 @@ int wxTextCtrl::GetLineLength(wxTextCoord line) const
     }
     else // multiline
     {
-        wxCHECK_MSG( (size_t)line < GetLineCount(), -1,
-                     wxT("line index out of range") );
+        if ( line < 0 || line >= GetLineCount() )
+            return -1;
 
         return GetLines()[line].length();
     }