fix: ensure log_offset is always valid in job SSE updates

- Wrap log_offset calculation with COALESCE to handle NULL case
- Ensures SSE clients always receive valid log offset (0 for new jobs)
- Fixes potential NULL values when job_logs table has no entries yet

Co-authored-by: Ruben Fiszel <rubenfiszel@users.noreply.github.com>

backend/windmill-api/src/jobs.rs

@@ -6092,7 +6092,7 @@ async fn get_job_update_data(
                 COALESCE(r.memory_peak, c.memory_peak) AS mem_peak,
                 COALESCE(c.flow_status, f.flow_status) AS \"flow_status: sqlx::types::Json<Box<RawValue>>\",
                 COALESCE(c.workflow_as_code_status, f.workflow_as_code_status) AS \"workflow_as_code_status: sqlx::types::Json<Box<RawValue>>\",
-                job_logs.log_offset + CHAR_LENGTH(job_logs.logs) + 1 AS log_offset,
+                COALESCE(job_logs.log_offset + CHAR_LENGTH(job_logs.logs) + 1, 0) AS log_offset,
                 created_by AS \"created_by!\",
                 CASE WHEN $4::BOOLEAN THEN (
                     SELECT scalar_int FROM job_stats WHERE job_id = $3 AND metric_id = 'progress_perc'