[zksend] handle spaces in hash (MystenLabs#15688)

## Description 

Describe the changes or additions included in this PR.

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

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

- [ ] protocol change
- [ ] 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

.changeset/empty-taxis-bathe.md

@@ -0,0 +1,5 @@
+---
+'@mysten/zksend': patch
+---
+
+Handle base64 with spaces in hash

sdk/zksend/src/channel/index.ts

@@ -99,7 +99,12 @@ export class ZkSendHost {
 		const parsed = new URL(url);
 
 		const urlHashData = parsed.hash
-			? Object.fromEntries(new URLSearchParams(parsed.hash.slice(1)))
+			? Object.fromEntries(
+					[...new URLSearchParams(parsed.hash.slice(1))].map(([key, value]) => [
+						key,
+						value.replace(/ /g, '+'),
+					]),
+			  )
 			: {};
 
 		const request = parse(ZkSendRequest, {

sdk/zksend/src/links.ts

@@ -138,7 +138,7 @@ export class ZkSendLinkBuilder {
 			} else {
 				const coins = (await this.#getCoinsByType(coinType)).map((coin) => coin.coinObjectId);
 				const merged =
-					coins.length > 0 ? txb.mergeCoins(coins[0], coins.slice(1)) : txb.object(coins[0]);
+					coins.length > 1 ? txb.mergeCoins(coins[0], coins.slice(1)) : txb.object(coins[0]);
 				const [split] = txb.splitCoins(merged, [amount]);
 				objectsToTransfer.push(split);
 			}