imgsz warning fix, download function consolidation (#681)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: HaeJin Lee <seareale@gmail.com>
Co-authored-by: Ayush Chaurasia <ayush.chaurarsia@gmail.com>

ultralytics/yolo/data/augment.py

@@ -44,8 +44,20 @@ class Compose:
         self.transforms = transforms
 
     def __call__(self, data):
+        mosaic_p = None
+        mosaic_imgsz = None
+
         for t in self.transforms:
-            data = t(data)
+            if isinstance(t, Mosaic):
+                temp = t(data)
+                mosaic_p = False if temp == data else True
+                mosaic_imgsz = t.imgsz
+                data = temp
+            else:
+                if isinstance(t, RandomPerspective):
+                    t.border = [-mosaic_imgsz // 2, -mosaic_imgsz // 2] if mosaic_p else [0, 0]
+                data = t(data)
+
         return data
 
     def append(self, transform):