[BUG] an extra empty line added with echo=true

[shg]

With doctype="multimarkdown", by weaving

```julia; echo=true
1
```

I get

```julia

1
```


```
1
```

You see an extra empty line before "1" in the echoed output. If I add a semicolon like

```julia; echo=true
1;
```

then the result does not contain the extra empty line.

```julia
1;
```

The extra empty line seems to be rendered with the other doctypes too (I haven't checked all of them though).

[ghost]

I have the same problem. It happens on github and pandoc doctypes too.

• Julia 1.5.2
• Weave v0.10.5
• Linux Mint 20 and Debian testing (occurs on both)

[aviatesk]

will be fixed in v0.10.6