generator: Fix whitespace.
generator: Fix the case where a daemon function has one FileIn/FileOut parameter and no other parameters.

The FileIn/FileOut parameters are not passed through to the daemon.
Previously we generated incorrect RPC code (an empty 'struct
guestfs_<fn>_args') because we didn't account for these FileIn/FileOut
parameters correctly.
src/file.c: Be sure to call guestfs___lazy_make_tmpdir before using g->tmpdir.

Although g->tmpdir is always set after launch, and none of these calls
should be used before launch, it's always possible that a caller would
use one of these APIs before launching the handle.

If guestfs___lazy_make_tmpdir is not called, then g->tmpdir is NULL,
and the constructed filename would look like "(null)/...".

In fact it's possible to observe this error (although it seems to have
no especially bad effects):

  $ strace guestfish ls / |& fgrep '(null)'
  unlink("(null)/ls1")     = -1 ENOENT (No such file or directory)