fix to check if the generated channel ID is not already stored

Signed-off-by: Jun Kimura <jun.kimura@datachain.jp>

Author: bluele

contracts/core/04-channel/IBCChannelHandshake.sol

@@ -55,6 +55,10 @@ contract IBCChannelHandshake is IBCModuleManager, IIBCChannelHandshake, IIBCChan
         }
 
         string memory channelId = generateChannelIdentifier();
+        ChannelStorage storage channelStorage = getChannelStorage()[msg_.portId][channelId];
+        if (channelStorage.channel.state != Channel.State.STATE_UNINITIALIZED_UNSPECIFIED) {
+            revert IBCChannelAlreadyChannelExists();
+        }
         initializeSequences(msg_.portId, channelId);
         emit GeneratedChannelIdentifier(channelId);
 
@@ -130,6 +134,10 @@ contract IBCChannelHandshake is IBCModuleManager, IIBCChannelHandshake, IIBCChan
         );
 
         string memory channelId = generateChannelIdentifier();
+        ChannelStorage storage channelStorage = getChannelStorage()[msg_.portId][channelId];
+        if (channelStorage.channel.state != Channel.State.STATE_UNINITIALIZED_UNSPECIFIED) {
+            revert IBCChannelAlreadyChannelExists();
+        }
         initializeSequences(msg_.portId, channelId);
         emit GeneratedChannelIdentifier(channelId);
 

contracts/core/04-channel/IIBCChannelErrors.sol

@@ -5,6 +5,8 @@ import {Height} from "../../proto/Client.sol";
 import {Channel} from "../../proto/Channel.sol";
 
 interface IIBCChannelErrors {
+    error IBCChannelAlreadyChannelExists();
+
     /// @param state channel state
     error IBCChannelUnexpectedChannelState(Channel.State state);