virJSONValueObjectGetStringArray: Report error if @key is not an array
virJSONValueObjectGetStringArray: Report error if @key is not an array

The virJSONValueObjectGetStringArray() function is given a @key
which is supposed to be an array inside given @object. Well, if
it's not then an error state is returned (NULL), but no error
message is set.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,zippy2/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,libvirt/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,jfehlig/libvirt