neoformat error when formatting nim file (nimpretty)
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## Expected behavior, english is required
Nim code should get formatted via nimpretty but error is raised instead.
Other "lang#nim" layer features seems to work correctly.

## The reproduce ways from Vim starting (Required!)
open any nim source file like
```nim
func asd: float = 5.0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
echo asd() 
```
do
`SPC b f`

format_on_save causes same error

## Debug info
```
Error detected while processing function neoformat#Neoformat[5]..<SNR>210_neoformat:                                                                                                                               
line   77:                                                                                                                                                                                                         
E482: Can't open file with an empty name
```
```
$ nim --version
1.4.8
```
```
$ nimpretty --version
0.2
```
```
$ cd .SpaceVim
$ git log --pretty=format:'%h' -n 1
8df089b5
```

running nimpretty manually works