Fix Conditionally rendered hook error in Buy with Fiat flow (#4211)

## Problem solved

Short description of the bug fixed or feature added

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---

## PR-Codex overview
This PR focuses on fixing a conditionally rendered hook error when buying funds using fiat.

### Detailed summary
- Added a new `onPostOnrampSuccess` function to handle successful post onramp swap
- Changed the logic to report fiat status instead of post onramp swap status after successful swap

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Author: MananTank

.changeset/thirty-bottles-jump.md

@@ -0,0 +1,5 @@
+---
+"thirdweb": patch
+---
+
+Fix Conditionally rendered hook error when Buying funds using fiat

packages/thirdweb/src/react/web/ui/ConnectWallet/screens/Buy/fiat/FiatFlow.tsx

@@ -68,6 +68,16 @@ export function FiatFlow(props: {
     props.openedWindow,
   );
 
+  const onPostOnrampSuccess = useCallback(() => {
+    // report the status of fiat status instead of post onramp swap status when post onramp swap is successful
+    getBuyWithFiatStatus({
+      intentId: props.quote.intentId,
+      client: props.client,
+    }).then((status) => {
+      props.onSuccess(status);
+    });
+  }, [props.onSuccess, props.quote.intentId, props.client]);
+
   if (screen.id === "step-1") {
     return (
       <FiatSteps
@@ -110,16 +120,6 @@ export function FiatFlow(props: {
     );
   }
 
-  const onPostOnrampSuccess = useCallback(() => {
-    // report the status of fiat status instead of post onramp swap status when post onramp swap is successful
-    getBuyWithFiatStatus({
-      intentId: props.quote.intentId,
-      client: props.client,
-    }).then((status) => {
-      props.onSuccess(status);
-    });
-  }, [props.onSuccess, props.quote.intentId, props.client]);
-
   if (screen.id === "postonramp-swap") {
     return (
       <PostOnRampSwapFlow