Invalid processing of the CSS shorthands

Currently using this plugin this stylesheet:
```
p {
color: %%styled-jsx-placeholder-1%%;
padding: %%styled-jsx-placeholder-2%%px %%styled-jsx-placeholder-2%%px;
}
```

Transforms into this:
```
p {
color: %%styled-jsx-placeholder-1%%;
padding: px %%styled-jsx-placeholder-2%%px;
}
```

Reproduce the issue by running the stylesheet shown in the report through the styled-jsx Sass plugin and compare the generated CSS with the expected shorthand. Confirm that both placeholder occurrences and their px units are preserved; the issue is done when the padding declaration remains valid after processing.

Written by the indexing model from the issue text.