[explorer] - fix UI display for missing timestamp in tx (MystenLabs#1…

…0923)

## Description 

Fixes displaying "0" when timestamp was empty

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

apps/explorer/src/pages/transaction-result/TransactionView.tsx

@@ -215,18 +215,14 @@ export function TransactionView({
                                         <StatAmount
                                             amount={formattedAmount}
                                             symbol={symbol}
-                                            date={Number(timestamp ?? 0)}
+                                            date={Number(timestamp)}
                                         />
                                     </section>
-                                ) : (
-                                    timestamp && (
-                                        <div className="mb-3">
-                                            <DateCard
-                                                date={Number(timestamp ?? 0)}
-                                            />
-                                        </div>
-                                    )
-                                )}
+                                ) : timestamp ? (
+                                    <div className="mb-3">
+                                        <DateCard date={Number(timestamp)} />
+                                    </div>
+                                ) : null}
                                 {isSponsoredTransaction && (
                                     <div className="mt-10">
                                         <SponsorTransactionAddress

apps/explorer/src/ui/StatAmount.tsx

@@ -15,7 +15,7 @@ export function StatAmount({ dollarAmount, date, ...props }: StatAmountProps) {
     return (
         <div className="flex flex-col justify-start gap-2 text-gray-75">
             <div className="flex flex-col items-baseline gap-2.5 text-gray-100">
-                {date && <DateCard date={date} />}
+                {date ? <DateCard date={date} /> : null}
                 <div className="flex flex-col items-baseline gap-2.5">
                     <Heading
                         as="h4"