[core/text] When stip is False allow space to remain on last line if it fits.

Fixes what @tito mentioned that when strip is False, a sentence forced across multiple lines will be indented by a single space. This fixes to allow the space to remain on the current line.

The problem is obvious when running the following code:

```
from kivy.app import runTouchApp
from kivy.lang import Builder

kv = '''
Label:
    text: 'I eat food ' * 5
    text_size: 100, None
'''

if __name__ == '__main__':
    runTouchApp(Builder.load_string(kv))

```