psbt: avoid a redundant keypath search for p2tr input signing

Author: jgriffiths

src/psbt.c

@@ -4642,19 +4642,14 @@ int wally_psbt_sign_input_bip32(struct wally_psbt *psbt,
         return WALLY_EINVAL;
 
     /* Find the public key this signature is for */
-    ret = wally_map_find_bip32_public_key_from(&inp->keypaths, subindex,
-                                               hdkey, &pubkey_idx);
-    if (ret != WALLY_OK || !pubkey_idx) {
-        /* Try again with the taproot public key */
+    if (is_taproot)
         ret = wally_map_find_bip32_public_key_from(&inp->taproot_leaf_hashes,
                                                    subindex, hdkey,
                                                    &pubkey_idx);
-        if (ret == WALLY_OK && pubkey_idx && !is_taproot)
-            return WALLY_EINVAL; /* Must be tr if we have a tr key */
-    } else if (ret == WALLY_OK && pubkey_idx && is_taproot) {
-        return WALLY_EINVAL; /* Must not be tr if we have a non-tr key */
-    }
-
+    else
+        ret = wally_map_find_bip32_public_key_from(&inp->keypaths,
+                                                   subindex, hdkey,
+                                                   &pubkey_idx);
     if (ret != WALLY_OK || !pubkey_idx)
         return WALLY_EINVAL; /* Signing pubkey key not found */