wrap try/finally around populateTransaction logic to ensure the lock is always released in the case of an error

ethers/signer.nim

@@ -103,6 +103,7 @@ method populateTransaction*(signer: Signer,
 
   var populated = transaction
 
+  try:
     if transaction.sender.isNone:
       populated.sender = some(await signer.getAddress())
     if transaction.chainId.isNone:
@@ -122,8 +123,6 @@ method populateTransaction*(signer: Signer,
         let e = getCurrentException()
         signer.decreaseNonce()
         raise e
-    finally:
-      signer.populateLock.release()
 
     else:
       if transaction.nonce.isNone:
@@ -131,6 +130,9 @@ method populateTransaction*(signer: Signer,
       if transaction.gasLimit.isNone:
         populated.gasLimit = some(await signer.estimateGas(populated))
 
+  finally:
+    signer.populateLock.release()
+
   return populated
 
 method cancelTransaction*(