fix: Add isFirst check before err check (#4326)

This was causing TestBlockNonBrowser to hang and fail.

codersdk/workspaceagents.go

@@ -331,6 +331,14 @@ func (c *Client) DialWorkspaceAgentTailnet(ctx context.Context, logger slog.Logg
 				// Need to disable compression to avoid a data-race.
 				CompressionMode: websocket.CompressionDisabled,
 			})
+			if isFirst {
+				if err != nil && res.StatusCode == http.StatusConflict {
+					first <- readBodyAsError(res)
+					return
+				}
+				isFirst = false
+				close(first)
+			}
 			if err != nil {
 				if errors.Is(err, context.Canceled) {
 					return
@@ -338,14 +346,6 @@ func (c *Client) DialWorkspaceAgentTailnet(ctx context.Context, logger slog.Logg
 				logger.Debug(ctx, "failed to dial", slog.Error(err))
 				continue
 			}
-			if isFirst {
-				if res.StatusCode == http.StatusConflict {
-					first <- readBodyAsError(res)
-					return
-				}
-				isFirst = false
-				close(first)
-			}
 			sendNode, errChan := tailnet.ServeCoordinator(websocket.NetConn(ctx, ws, websocket.MessageBinary), func(node []*tailnet.Node) error {
 				return conn.UpdateNodes(node)
 			})