pg_restore --format= option(without any value) should report an error as pg_dump is reporting an error

Hi,
With "pg_restore --format=", we are not giving any error because in code,
we are checking length of arg but pg_dump is reporting an error for the
same option.

For the consistency purpose, pg_dump and pg_restore both should report an
error for the test case below.

*Ex: (output after this patch)but before this patch, below command is
passing.*
/pg_restore x1 -d postgres -j 10 -C --verbose --format=
pg_restore: error: unrecognized archive format ""; please specify "c", "d",
or "t"

Here, I am attaching a patch which is fixing the same. I added 2 TAP tests
also for invalid options.

*Note:* We have 2 more options in pg_restore code which validate the option
if arg has non zero length. I will prepare patches for both(--host and
--port). We need to add some validate function also for both these options.

--
Thanks and Regards
Mahendra Singh Thalor
EnterpriseDB: http://www.enterprisedb.com