[Bug] fix for module_has_exports (#50680)
Summary:
The attributes in `dir(mod)` may not be valid, this will throw error when calling `getattr`.
Use `hasattr` to test if it is valid.
Here is an example:
```python
class A:
def __init__(self, x):
if x:
self._attr = 1
property
def val(self):
return getattr(self, '_attr')
a = A(False)
print('val' in dir(a))
print(hasattr(a, 'val'))
b = A(True)
print('val' in dir(b))
print(hasattr(b, 'val'))
```
And the outputs:
```
True
False
True
True
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50680
Reviewed By: malfet
Differential Revision: D26103975
Pulled By: eellison
fbshipit-source-id: 67a799afe7d726153c91654d483937c5e198ba94
