Regression: unsaved buffers are not executed if they contain more than one line

The buffer language is set to Python, but if there is more than one line, the code does not seem to be executed. For example:

``` python
print(1)
print(2)
```

The above code will have no output, only `[Finished in 0.072s]`.

If only `print(1)` is in the buffer, the output is:

```
1
[Finished in 0.072s]
```

The bug appeared in the last few months (unsure about the exact version), older versions worked correctly.