remote: avoid null dereference on error

remote: avoid null dereference on error

Clang found three instances of uninitialized use of nparams in
the cleanup path.  Unfortunately, one is a false positive: clang
couldn't see that ret->params.params_val is guaranteed to be
NULL unless allocated within a function, and that nparams is
guaranteed to be assigned prior to the allocation; hoisting the
assignment to nparams to be earlier in the function shuts up
that false positive.  But two of the reports also happened to
highlight a real bug - the error path can dereference NULL.

Regression introduced in commit 158ba873.

* daemon/remote.c (remoteDispatchDomainGetMemoryParameters)
(remoteDispatchDomainGetBlkioParameters): Don't clear fields if
array was not allocated.
(remoteDispatchDomainGetSchedulerParameters): Initialize nparams
earlier.