Update Detect() grid init `for` loop (#9494)

models/yolo.py

@@ -47,8 +47,8 @@ class Detect(nn.Module):
         self.no = nc + 5  # number of outputs per anchor
         self.nl = len(anchors)  # number of detection layers
         self.na = len(anchors[0]) // 2  # number of anchors
-        self.grid = [torch.empty(1)] * self.nl  # init grid
-        self.anchor_grid = [torch.empty(1)] * self.nl  # init anchor grid
+        self.grid = [torch.empty(0) for _ in range(self.nl)]  # init grid
+        self.anchor_grid = [torch.empty(0) for _ in range(self.nl)]  # init anchor grid
         self.register_buffer('anchors', torch.tensor(anchors).float().view(self.nl, -1, 2))  # shape(nl,na,2)
         self.m = nn.ModuleList(nn.Conv2d(x, self.no * self.na, 1) for x in ch)  # output conv
         self.inplace = inplace  # use inplace ops (e.g. slice assignment)