vbo/dlist: add vertices to incomplete primitives
If a primitive is added with missing vertices, this will shift all the vertices and produce incorrect rendering. In issue #5786 the app uses GL_LINE_STRIPS with a single vertex. Adding extra vertices can make the initial estimation for the index buffer size incorrect, so this buffer can now be growed if needed. Fixes: ac3d4c76 ("vbo/dlist: convert LINE_STRIPS to LINES") Closes: mesa/mesa#5786 Acked-by:Marek Olšák <marek.olsak@amd.com> Part-of: <mesa/mesa!14476> (cherry picked from commit dcbf2423)