Releases all memory associated with a
GVariantDict without freeing
GVariantDict structure itself.
It typically only makes sense to do this on a stack-allocated
GVariantDict if you want to abort building the value part-way
through. This function need not be called if you call
g_variant_dict_end() and it also doesn’t need to be called on dicts
allocated with g_variant_dict_new (see
g_variant_dict_unref() for that).
It is valid to call this function on either an initialised
GVariantDict or one that was previously cleared by an earlier call
g_variant_dict_clear() but it is not valid to call this function
on uninitialised memory.