All-zero category leads to empty plot

[salim-b]

Description

When a category of the input time series data is always zero, ggstream fails to produce a plot.

Reproducible example

ggstream::blockbusters |>
    dplyr::mutate(box_office = dplyr::if_else(genre == "Action",
                                              0,
                                              box_office)) |>
    ggplot2::ggplot(mapping = ggplot2::aes(x = year,
                                           y = box_office,
                                           fill = genre)) +
    ggstream::geom_stream()

^{Created on 2023-04-21 with reprex v2.0.2}

Expected result

I'd expect the example above to produce the same result as...

ggstream::blockbusters |>
    dplyr::filter(genre != "Action")|>
    ggplot2::ggplot(mapping = ggplot2::aes(x = year,
                                           y = box_office,
                                           fill = genre)) +
    ggstream::geom_stream()

...but with an additional legend entry for the Action category.

^{Created on 2023-04-21 with reprex v2.0.2}