ultralytics 8.0.206 engine Trainer updates (#6111)

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: jamjamjon <51357717+jamjamjon@users.noreply.github.com>

ultralytics/utils/checks.py

@@ -426,6 +426,14 @@ def check_yolov5u_filename(file: str, verbose: bool = True):
     return file
 
 
+def check_model_file_from_stem(model='yolov8n'):
+    """Return a model filename from a valid model stem."""
+    if model and not Path(model).suffix and Path(model).stem in downloads.GITHUB_ASSETS_STEMS:
+        return Path(model).with_suffix('.pt')  # add suffix, i.e. yolov8n -> yolov8n.pt
+    else:
+        return model
+
+
 def check_file(file, suffix='', download=True, hard=True):
     """Search/download file (if necessary) and return path."""
     check_suffix(file, suffix)  # optional