reading uninitialized buffer

I've been testing pg using valgrind and have found a read of an
uninitialized buffer. In the hba-tokenizer when we have not read any
characters (or too few) we still perform a couple of:

   strncmp(start_buf,"sameuser",8)

Since this is done on random data it might return true although we have
not read anything. The result is that we can (even if the probability is
low) return the wrong thing.

The solution is simply to terminate the buffer with '\0' before the 
strncmp().

I also moved our test inside the previous if, outside of that block our
test can never be true anyway. I don't know why it was outside in the 
first place.

-- 
/Dennis Björklund