Check .ino sketch file exists in path before creating a new one

Running "arduino-cli sketch new ." from a sketch directory overwrites an existing .ino sketch file, without asking for confirmation. This fix introduces a check to verify if the specified path already
contains a .ino sketch file. If it does, an error is returned, otherwise a new sketch is created as usual.

Author: MatteoPologruto

Diff for: commands/sketch/new.go

@@ -17,6 +17,7 @@ package sketch
 
 import (
 	"context"
+	"errors"
 
 	"github.com/arduino/arduino-cli/arduino"
 	"github.com/arduino/arduino-cli/arduino/globals"
@@ -47,6 +48,9 @@ func NewSketch(ctx context.Context, req *rpc.NewSketchRequest) (*rpc.NewSketchRe
 	}
 	sketchName := sketchDirPath.Base()
 	sketchMainFilePath := sketchDirPath.Join(sketchName + globals.MainFileValidExtension)
+	if sketchMainFilePath.Exist() {
+		return nil, &arduino.CantCreateSketchError{Cause: errors.New(".ino file already exists")}
+	}
 	if err := sketchMainFilePath.WriteFile(emptySketch); err != nil {
 		return nil, &arduino.CantCreateSketchError{Cause: err}
 	}