service/dap: fix bugs in stdout/stderr handling (#3522)

Fixes bugs introduced in v1.21.1

* Avoid dropping the last bytes from stderr/stdout when Read returns an
  error. (Read returns n>0). And skip sending Output event if Read
  returns n==0.

* Fix the bug that drops all stdout in the existing noDebug mode.

For #3253

service/dap/server.go

@@ -1050,13 +1050,7 @@ func (s *Session) onLaunchRequest(request *dap.LaunchRequest) {
 			var out [1024]byte
 			for {
 				n, err := reader.Read(out[:])
-				if err != nil {
+				if n > 0 {
-					if err == io.EOF {
-						return
-					}
-					s.config.log.Errorf("failed read by %s - %v ", category, err)
-					return
-				}
 					outs := string(out[:n])
 					s.send(&dap.OutputEvent{
 						Event: *newEvent("output"),
@@ -1065,6 +1059,14 @@ func (s *Session) onLaunchRequest(request *dap.LaunchRequest) {
 							Category: category,
 						}})
 				}
+				if err != nil {
+					if err == io.EOF {
+						return
+					}
+					s.config.log.Errorf("failed read by %s - %v ", category, err)
+					return
+				}
+			}
 		}
 
 		s.preTerminatedWG.Add(2)
@@ -1186,7 +1188,7 @@ func (s *Session) newNoDebugProcess(program string, targetArgs []string, wd stri
 			return nil, err
 		}
 	} else {
-		cmd.Stdout, cmd.Stderr = os.Stdin, os.Stderr
+		cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
 	}
 
 	if err = cmd.Start(); err != nil {