Failure of Rmd cell parsing with #''' in code cell

[matthew-brett]

I ran into the following odd failure with current Jupytext (1.14.5). Consider the following .Rmd text:

```{python}
 #'''
```

```{python}
# Another cell
```

Notice the space before the first # above.

When converting to .ipynb, Jupytext does not separate the two cells. Deleting the leading space or one of the three single quotes fixes the conversion. There is no change in behavior for any amount of extra whitespace in front of the #. It doesn't appear to matter if there is any text before or after the '''.