fix CreateTransaction error messages

src/wallet/wallet.cpp

@@ -2238,7 +2238,7 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
     {
         if (nValue < 0 || recipient.nAmount < 0)
         {
-            strFailReason = _("Transaction amounts must be positive");
+            strFailReason = _("Transaction amounts must not be negative");
             return false;
         }
         nValue += recipient.nAmount;
@@ -2246,9 +2246,9 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
         if (recipient.fSubtractFeeFromAmount)
             nSubtractFeeFromAmount++;
     }
-    if (vecSend.empty() || nValue < 0)
+    if (vecSend.empty())
     {
-        strFailReason = _("Transaction amounts must be positive");
+        strFailReason = _("Transaction must have at least one recipient");
         return false;
     }