Fixup jumpToLocation loc.file is NoneType

Signed-off-by: visitor83 <wolflouiswang@gmail.com>
Error message as follows, then find out the libclang.py gotoDeclaration have some error
```python
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/root/.vim/plugin/libclang.py", line 547, in gotoDeclaration
    jumpToLocation(loc.file.name, loc.line, loc.column)
AttributeError: 'NoneType' object has no attribute 'name'
```