added shape checking to WeightedRandomSampler (#78585)
Fixes #78236
An erronously shaped weights vector will result in the following output
```
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
~/datarwe/pytorch/torch/utils/data/sampler.py in <module>
[274](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=273) WeightedRandomSampler([1,2,3], 10)
----> [275](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=274) WeightedRandomSampler([[1,2,3], [4,5,6]], 10)
~/datarwe/pytorch/torch/utils/data/sampler.py in __init__(self, weights, num_samples, replacement, generator)
[192](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=191) weights = torch.as_tensor(weights, dtype=torch.double)
[193](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=192) if len(weights.shape) != 1:
--> [194](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=193) raise ValueError("weights should be a 1d sequence but given "
[195](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=194) "weights have shape {}".format(tuple(weights.shape)))
[196](file:///home/oliver/datarwe/pytorch/torch/utils/data/sampler.py?line=195)
ValueError: weights should be a 1d sequence but given weights have shape (2, 3)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78585
Approved by: https://github.com/NivekT, https://github.com/ejguan
