fix(Animation): not to throw if children is not set

[mnajdova]

Fixes #2341

[miroslavstastny]

no UT?

[DustyTheBot]

Perf comparison

Status	Scenario	Fluent TPI	Fabric TPI	Ratio	Iterations	Ticks
🔧	Avatar.Fluent	0.48	0.39	1.23:1	2000	951
🎯	Button.Fluent	0.13	0.17	0.76:1	1000	127
🔧	Checkbox.Fluent	0.79	0.28	2.82:1	1000	793
🔧	Dialog.Fluent	0.32	0.17	1.88:1	5000	1587
🔧	Dropdown.Fluent	3.31	0.35	9.46:1	1000	3310
🔧	Icon.Fluent	0.11	0.03	3.67:1	5000	573
🎯	Image.Fluent	0.05	0.07	0.71:1	5000	232
🔧	Slider.Fluent	1.37	0.31	4.42:1	1000	1369
🔧	Text.Fluent	0.06	0.02	3:1	5000	279
🦄	Tooltip.Fluent	0.14	17.94	0.01:1	5000	676

🔧 Needs work     🎯 On target     🦄 Amazing

Perf tests with no regressions

Scenario	Current PR Ticks	Baseline Ticks	Ratio
ProviderMergeThemesPerf.default	1245	1080	1.15:1
SegmentMinimalPerf.default	1394	1211	1.15:1
AccordionMinimalPerf.default	208	185	1.12:1
ButtonMinimalPerf.default	119	106	1.12:1
AnimationMinimalPerf.default	516	463	1.11:1
DropdownManyItemsPerf.default	457	410	1.11:1
SliderMinimalPerf.default	1505	1354	1.11:1
PopupMinimalPerf.default	361	327	1.1:1
InputMinimalPerf.default	975	898	1.09:1
PortalMinimalPerf.default	246	226	1.09:1
Text.Fluent	279	257	1.09:1
AlertMinimalPerf.default	645	599	1.08:1
HeaderMinimalPerf.default	511	481	1.06:1
HeaderSlotsPerf.default	1434	1348	1.06:1
CustomToolbarPrototype.default	3761	3543	1.06:1
Tree60WithListItems.default	215	203	1.06:1
Tooltip.Fluent	676	635	1.06:1
BoxMinimalPerf.default	222	212	1.05:1
AvatarMinimalPerf.default	551	528	1.04:1
DialogMinimalPerf.default	1660	1591	1.04:1
ReactionMinimalPerf.default	2698	2602	1.04:1
TextMinimalPerf.default	253	244	1.04:1
ImageMinimalPerf.default	235	229	1.03:1
LabelMinimalPerf.default	826	801	1.03:1
Icon.Fluent	573	554	1.03:1
ListCommonPerf.default	158	155	1.02:1
AttachmentSlotsPerf.default	3449	3421	1.01:1
ChatMinimalPerf.default	1688	1678	1.01:1
DropdownMinimalPerf.default	3560	3515	1.01:1
FormMinimalPerf.default	740	736	1.01:1
RadioGroupMinimalPerf.default	430	427	1.01:1
CarouselMinimalPerf.default	1830	1832	1:1
Dropdown.Fluent	3310	3324	1:1
ChatDuplicateMessagesPerf.default	524	528	0.99:1
SplitButtonMinimalPerf.default	11497	11632	0.99:1
ToolbarMinimalPerf.default	691	696	0.99:1
CheckboxMinimalPerf.default	3507	3592	0.98:1
ItemLayoutMinimalPerf.default	1760	1802	0.98:1
MenuMinimalPerf.default	1995	2041	0.98:1
ProviderMinimalPerf.default	546	558	0.98:1
TableMinimalPerf.default	550	559	0.98:1
EmbedMinimalPerf.default	6332	6549	0.97:1
ListMinimalPerf.default	270	278	0.97:1
VideoMinimalPerf.default	667	691	0.97:1
ChatWithPopoverPerf.default	542	563	0.96:1
TreeMinimalPerf.default	856	888	0.96:1
Button.Fluent	127	132	0.96:1
Checkbox.Fluent	793	826	0.96:1
TextAreaMinimalPerf.default	2888	3034	0.95:1
Avatar.Fluent	951	1006	0.95:1
Dialog.Fluent	1587	1679	0.95:1
ButtonSlotsPerf.default	568	607	0.94:1
LoaderMinimalPerf.default	2315	2459	0.94:1
TooltipMinimalPerf.default	827	879	0.94:1
AttachmentMinimalPerf.default	906	976	0.93:1
MenuButtonMinimalPerf.default	1500	1608	0.93:1
DividerMinimalPerf.default	865	940	0.92:1
IconMinimalPerf.default	298	326	0.91:1
Slider.Fluent	1369	1506	0.91:1
HierarchicalTreeMinimalPerf.default	818	931	0.88:1
LayoutMinimalPerf.default	488	562	0.87:1
StatusMinimalPerf.default	225	259	0.87:1
GridMinimalPerf.default	865	1025	0.84:1
Image.Fluent	232	279	0.83:1
FlexMinimalPerf.default	357	440	0.81:1
RefMinimalPerf.default	144	180	0.8:1

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