[editor] Fix editor by removing pointless variable reassignment

Fix editor by removing pointless variable reassignment on contiguous lines,

https://github.com/ninja-ide/ninja-ide/blob/master/ninja_ide/gui/editor/editor.py#L100     

```python
 self.__lines_count = None  
```

y dos lineas despues

```python
self.__lines_count = 0
```

Brancho: fix/editor  :yum: