backport of
https://github.com/love2d/love/commit/b2785df4373f0af13b0e3d518badae2f2beae8c5.patch

Index: src/modules/graphics/Polyline.cpp
--- src/modules/graphics/Polyline.cpp.orig
+++ src/modules/graphics/Polyline.cpp
@@ -100,7 +100,7 @@ void Polyline::render(const Vector2 *coords, size_t co
 	}
 
 	// Add the degenerate triangle strip.
-	if (extra_vertices)
+	if (extra_vertices && vertex_count > 0)
 	{
 		vertices[vertex_count + 0] = vertices[vertex_count - 1];
 		vertices[vertex_count + 1] = vertices[overdraw_vertex_start];
