Silence warning about uninitialized 'ret' variable on some compilers.

Silence warning about uninitialized 'ret' variable on some compilers.

If the compiler doesn't notice that the switch-statement handles all
possible values of the enum, it might complain that 'ret' is being used
without initialization. Jeff Janes reported that on gcc 4.4.7.

Discussion: https://www.postgresql.org/message-id/CAMkU=1x31RvP+cpooFbmc8K8nt-gNO8woGFhXcgQYYZ5ozYpFA@mail.gmail.com