chore(protocol): avoid transfer to self in assignment hook (#16696)

Author: dantaik

packages/protocol/contracts/L1/TaikoData.sol

@@ -110,7 +110,7 @@ library TaikoData {
     }
 
     /// @dev Struct containing data required for verifying a block.
-    /// 10 slots reserved for upgradability, 3 slots used.
+    /// 3 slots used.
     struct Block {
         bytes32 metaHash; // slot 1
         address assignedProver; // slot 2

packages/protocol/contracts/L1/hooks/AssignmentHook.sol

@@ -118,11 +118,11 @@ contract AssignmentHook is EssentialContract, IHook {
         // The proposer irrevocably pays a fee to the assigned prover, either in
         // Ether or ERC20 tokens.
         if (assignment.feeToken == address(0)) {
-            // Paying Ether
+            // Paying Ether even when proverFee is 0 to trigger a potential receive() function call.
             // Note that this payment may fail if it cost more gas
             bool success = _blk.assignedProver.sendEther(proverFee, MAX_GAS_PAYING_PROVER, "");
             if (!success) emit EtherPaymentFailed(_blk.assignedProver, MAX_GAS_PAYING_PROVER);
-        } else if (proverFee != 0) {
+        } else if (proverFee != 0 && _meta.sender != _blk.assignedProver) {
             // Paying ERC20 tokens
             IERC20(assignment.feeToken).safeTransferFrom(
                 _meta.sender, _blk.assignedProver, proverFee