fix(generator): improve LLM response handling logic

- restructure response processing for clarity
- handle error status with specific error messages
- ensure callback is called for all response cases
- add missing handler comment for LLM response

Author: jinzhongjia

lua/codecompanion/_extensions/gitcommit/generator.lua

@@ -106,6 +106,7 @@ Generate commit message for this diff:
   )
 end
 
+---Handle LLM response
 ---@param err table|nil Error from request
 ---@param data table|nil Response data
 ---@param adapter table The adapter used
@@ -122,25 +123,25 @@ function Generator._handle_response(err, data, adapter, callback)
     return callback(nil, "No response received from LLM")
   end
 
-  -- Process the LLM response
-  local result = _adapter.handlers.chat_output(_adapter, data)
-  if not (result and result.status) then
-    return callback(nil, "No valid response received")
-  end
-
-  if result.status == CONSTANTS.STATUS_SUCCESS then
-    local content = result.output and result.output.content
-    if content and vim.trim(content) ~= "" then
-      return callback(vim.trim(content), nil)
-    else
-      return callback(nil, "Generated content is empty")
+  -- Process successful response
+  if data then
+    local result = adapter.handlers.chat_output(adapter, data)
+    if result and result.status then
+      if result.status == CONSTANTS.STATUS_SUCCESS then
+        local content = result.output and result.output.content
+        if content and vim.trim(content) ~= "" then
+          return callback(vim.trim(content), nil)
+        else
+          return callback(nil, "Generated content is empty")
+        end
+      elseif result.status == CONSTANTS.STATUS_ERROR then
+        local error_msg = result.output or "Unknown error occurred"
+        return callback(nil, error_msg)
+      end
     end
-  elseif result.status == CONSTANTS.STATUS_ERROR then
-    local error_msg = result.output or "Unknown error occurred"
-    return callback(nil, error_msg)
-  else
-    return callback(nil, "Unexpected response status: " .. tostring(result.status))
   end
+
+  return callback(nil, "No valid response received")
 end
 
 return Generator