PVS-Studio warning V614 for Firebird

static const UCHAR* compile(const UCHAR* sdl, sdl_arg* arg)
{
  SLONG n, count, variable, value, sdl_operator;
  ....
  switch (op)
  {
    ....
    case isc_sdl_add:
      sdl_operator = op_add;
    case isc_sdl_subtract:
      if (!sdl_operator)
        sdl_operator = op_subtract;
  ......
}

This suspicious code was found in Firebird project by PVS-Studio static code analyzer.
Warning message is:
V614 Uninitialized variable 'sdl_operator' used. sdl.cpp 404

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/