Drop shadows don't appear on horizontal and vertical lines

[Bartosz Leper]

Reproduction steps:

1. Create a new document.
2. Draw a horizontal or vertical line using "Draw Bezier curves and straight lines" tool. Use Ctrl key to make sure it's horizontal or vertical.
3. Use Filters|Shadows and Glows|Drop shadow..., accept the default settings.

Expected result: a shadow should appear under the line.
Actual result: no shadow until I slightly affect the line angle.

I'm using 0.48.4 r9939 on Ubuntu 14.04.2. I'm attaching an example and a screenshot.

[su_v (suv-lp)]

To be expected (based on the description of filter effects in the current SVG 1.1 specification - the filter effects region is expressed in percentage of the geometric bounding box area of the filtered object - a horizontal or vertical line has zero height or width respectively, and the filter effect region thus too).

Known issue already tracked in
* Bug #168943 “Blurring a zero-height or zero-width path”
  https://bugs.launchpad.net/inkscape/+bug/168943

Linking as duplicate to bug #168943 (see comment 1-2 there).

[Bartosz Leper (bl-nero)]

For anyone stumbling across a similar problem, I found a workaround:

1. Create a transparent rectangle with transparent stroke (i.e. an invisible one) so that it covers the line in question.
2. Group the rectangle with line.
3. Apply the shadow effect to the entire group.