Convert to dashes bug if stroke-dasharray has 0

Summary:

If the first value in stroke-dasharray is 0 such as when drawing a line of dots (e.g. stroke-dasharray:0,1), then the 'Extensions -> Modify path -> Convert to dashes' operation fails to convert each dot into a subpath.

Steps to reproduce:

• Open Inkscape
• Draw dotted line
  • Draw line segment (B, click two points, Enter)
  • Open 'Object -> Fill and Stroke -> Stroke style'
  • Select the first dashed line in 'Dashes'
  • Change 'Pattern' from 1 1 to 0 4
  • Change 'Cap' from 'Butt Cap' to 'Round Cap'
• Convert each dot into a subpath
  • Open 'Extensions -> Modify path -> Convert to dashes'

What happened?

Dotted line segment disappears completely in both Inkscape's GUI and in exported PDFs. XML Editor shows the path object exists with some subpath info but nothing is displayed. Note: Firefox 91.6.0esr still displays the line segment.

What should have happened?

The dotted line segment should have stayed visible.

A kludgey workaround I found is to change the 0 to something small but non-zero (e.g. in 'Stroke style -> Pattern', change 0 4 to 0.01 4).

example	example-failed	example-kludge
Example state before Convert to dashes	Convert to dashes result	Convert do dashes result if using 0 4 -> 0.01 4 kludge
example.svg, example.pdf	example-failed.svg, example-failed.pdf	example-kludge.svg, example-kludge.pdf

Note: I have encountered several instances of Inkscape importing .eps files from academic sources with stroke-dasharray containing 0 values for dotted lines. I suspect there is a divide-by-zero error in extensions/convert2dashes.py when parsing stroke-dasharray values. This bug could be ignored if you argue a dot can't technically be made a path since paths need at least two points, but I'd argue a normal user shouldn't be expected to care too much about this difference; I still think it's a bug.

Version info

Inkscape 1.2-alpha1 (9465ba4, 2022-02-23)

    GLib version:     2.64.6
    GTK version:      3.24.20
    glibmm version:   2.64.2
    gtkmm version:    3.24.2
    libxml2 version:  2.9.10
    libxslt version:  1.1.34
    Cairo version:    1.17.4
    Pango version:    1.44.7
    HarfBuzz version: 2.6.4

    OS version:       Debian GNU/Linux 10 (buster)