feat: enhance error handling in GeminiHelper and streamline response processing

- Added status code mapping handling in GeminiHelper to reset status codes based on response.
- Removed redundant candidate check in GeminiTextGenerationHandler to simplify response processing.

relay/relay-gemini.go

@@ -165,8 +165,23 @@ func GeminiHelper(c *gin.Context) (openaiErr *dto.OpenAIErrorWithStatusCode) {
 		return service.OpenAIErrorWrapperLocal(err, "do_request_failed", http.StatusInternalServerError)
 	}
 
+	statusCodeMappingStr := c.GetString("status_code_mapping")
+
+	var httpResp *http.Response
+	if resp != nil {
+		httpResp = resp.(*http.Response)
+		relayInfo.IsStream = relayInfo.IsStream || strings.HasPrefix(httpResp.Header.Get("Content-Type"), "text/event-stream")
+		if httpResp.StatusCode != http.StatusOK {
+			openaiErr = service.RelayErrorHandler(httpResp, false)
+			// reset status code 重置状态码
+			service.ResetStatusCode(openaiErr, statusCodeMappingStr)
+			return openaiErr
+		}
+	}
+
 	usage, openaiErr := adaptor.DoResponse(c, resp.(*http.Response), relayInfo)
 	if openaiErr != nil {
+		service.ResetStatusCode(openaiErr, statusCodeMappingStr)
 		return openaiErr
 	}