Fix misleading error message when user token is unavailable (#225)

It fixes #224 
## Test plan
* Add account on one version of IJ
* Open another version of IJ with cody installed
* Deny access to keychain
* Prompt about adding missing token should be displayed


https://github.com/sourcegraph/jetbrains/assets/9321940/ff5f7923-875d-40a1-bcdf-81f38c0f8bd7


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src/main/kotlin/com/sourcegraph/cody/CodyToolWindowContent.kt

@@ -142,7 +142,10 @@ class CodyToolWindowContent(private val project: Project) : UpdatableChat {
         agentUserId = getUserId(server)
       }
       if (jetbrainsUserId != agentUserId) {
-        logger.error("User id in JetBrains is different from agent")
+        if (agentUserId != null) {
+          logger.error("User id in JetBrains is different from agent")
+          return
+        }
         return
       }