solana sdk: Fix getIsApproved to check inbox item (#550)

* solana sdk: Fix getIsApproved to check inbox item

getIsApproved() was returning true when the VAA was posted, causing
track() to set the receipt state to DestinationInitiated prematurely.
It should check if the inbox item is initialized instead.

Fixes an issue that caused calls to NttManualRoute.complete() to
return early and never actually complete the transfer in rare cases
(receipt.DestinationInitiated === true and inbox item not created).

* throw instead of return false

solana/ts/sdk/ntt.ts

@@ -800,14 +800,22 @@ export class SolanaNtt<N extends Network, C extends SolanaChains>
   }
 
   async getIsApproved(attestation: Ntt.Attestation): Promise<boolean> {
-    const digest = (attestation as WormholeNttTransceiver.VAA).hash;
-    const vaaAddress = utils.derivePostedVaaKey(
-      this.core.address,
-      Buffer.from(digest)
-    );
-
-    const info = await this.connection.getAccountInfo(vaaAddress);
-    return info !== null;
+    if (attestation.payloadName !== "WormholeTransfer") {
+      throw new Error(`Invalid payload: ${attestation.payloadName}`);
+    }
+    const payload = attestation.payload["nttManagerPayload"];
+    try {
+      // check that the inbox item was initialized
+      const inboxItem = await this.program.account.inboxItem.fetch(
+        this.pdas.inboxItemAccount(attestation.emitterChain, payload)
+      );
+      return inboxItem.init;
+    } catch (e: any) {
+      if (e.message?.includes("Account does not exist")) {
+        return false;
+      }
+      throw e;
+    }
   }
 
   async *completeInboundQueuedTransfer(