Do not create new chat session when an old chat session is deleted

- Fix
  `get_conversation_by_user' shouldn't return new conversation if
  conversation with requested id not found.

  It should only return new conversation if no specific conversation
  is requested and no conversations found for user at all

- Repro
  - Delete a new chat, this calls loadChat via window.onload which
    calls server /chat/history API endpoint with conversationId set to
    that of just deleted conversation sporadically

    The call to GET chat/history API with conversationId set occurs
    when window.onload triggers before the conversationId is deleted
    by the delete button after the DELETE /chat/history API call (via race)

  - In such a scenario, get_conversation_by_user called by
    chat/history API with conversationId of deleted conversation
    returns a new conversation

- Miscellaneous
  - Chat history load should be logged as call to that chat_history api,
    not the "chat" api
  - Show status updates of clearing conversation history in chat input
  - Simplify web, desktop client code by removing unnecessary new variables

src/interface/desktop/chat.html

@@ -626,10 +626,9 @@
 
             let chatBody = document.getElementById("chat-body");
             chatBody.innerHTML = "";
-            let conversationId = chatBody.dataset.conversationId;
             let chatHistoryUrl = `/api/chat/history?client=desktop`;
-            if (conversationId) {
-                chatHistoryUrl += `&conversation_id=${conversationId}`;
+            if (chatBody.dataset.conversationId) {
+                chatHistoryUrl += `&conversation_id=${chatBody.dataset.conversationId}`;
             }
 
             fetch(`${hostURL}${chatHistoryUrl}`, { headers })
@@ -650,6 +649,8 @@
                         // Disable chat input field and update placeholder text
                         document.getElementById("chat-input").setAttribute("disabled", "disabled");
                         document.getElementById("chat-input").setAttribute("placeholder", "Configure Khoj to enable chat");
+                    } else if (data.status != "ok") {
+                        throw new Error(data.message);
                     } else {
                         // Set welcome message on load
                         renderMessage("Hey 👋🏾, what's up?", "khoj");
@@ -657,12 +658,9 @@
                     return data.response;
                 })
                 .then(response => {
-                    conversationId = response.conversation_id;
-                    const conversationTitle = response.slug || `New conversation 🌱`;
-
                     let chatBody = document.getElementById("chat-body");
-                    chatBody.dataset.conversationId = conversationId;
-                    chatBody.dataset.conversationTitle = conversationTitle;
+                    chatBody.dataset.conversationId = response.conversation_id;
+                    chatBody.dataset.conversationTitle = response.slug || `New conversation 🌱`;
 
                     const fullChatLog = response.chat || [];
 
@@ -791,7 +789,7 @@
                     chatBody.dataset.conversationId = "";
                     chatBody.dataset.conversationTitle = "";
                     loadChat();
-                    flashStatusInChatInput("🗑 Cleared conversation history");
+                    flashStatusInChatInput("🗑 Cleared previous conversation history");
                 })
                 .catch(err => {
                     flashStatusInChatInput("⛔️ Failed to clear conversation history");