[#307] v2/storagegroup/test: Do not allocate memory if `!empty`

Move all memory allocation and field settings
in `Generate...(empty bool)` functions behind
`if !empty` check.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

v2/storagegroup/test/generate.go

@@ -11,10 +11,10 @@ func GenerateStorageGroup(empty bool) *storagegroup.StorageGroup {
 	if !empty {
 		m.SetValidationDataSize(44)
 		m.SetExpirationEpoch(55)
+		m.SetMembers(refstest.GenerateObjectIDs(false))
 	}
 
 	m.SetValidationHash(refstest.GenerateChecksum(empty))
-	m.SetMembers(refstest.GenerateObjectIDs(empty))
 
 	return m
 }