title: DrawOptions error with DampedSpring between Body and StaticBody
body: <p>my goal is to reproduce a top down physic system in which given two bodies B1 and B2, when B1 hits B2 then B2 oppose resistance and tries to get back to the initial position.</p>
  <p>Something like this:</p>
  <pre><code>t = 0       B2      B1
  t = 0       B2    B1
  t = 0       B2   B1
  t = 0       B2 B1
  t = 0      B2B1
  t = 0     B2B1
  t = 0    B2B1
  t = 0     B2B1
  t = 0      B2B1
  t = 0       B2B1
  </code></pre>
  <p>I managed to obtain this effect by connecting B2 with the initial position using a DampedSpring and the static body.</p>
  <p>The code can be found at <a href="https://gist.github.com/MichelangeloConserva/9e0fd824053c41c7fc9845a769e8b083" rel="nofollow noreferrer">gist link</a></p>
  <p>This is what the result of the code looks like
  <img src="https://user-images.githubusercontent.com/37903256/88177447-c8e9b280-cc20-11ea-95a8-ef2eb460b35b.gif" alt="collision_test" />
  When the body becomes green then the DumpedSpring is added.</p>
  <p>However there is one big issue.
  If I use <em>DrawOptions</em> to draw pymunk objects then I get the following error:</p>
  <pre><code>From cffi callback &lt;function SpaceDebugDrawOptions.__init__.&lt;locals&gt;.f2 at 0x7f0540918f80&gt;:
  Traceback (most recent call last):
    File &quot;/home/michelangelo/miniconda3/envs/main/lib/python3.7/site-packages/pymunk/space_debug_draw_options.py&quot;, line 74, in f2
      Vec2d._fromcffi(a), Vec2d._fromcffi(b), self._c(color))
    File &quot;/home/michelangelo/miniconda3/envs/main/lib/python3.7/site-packages/pymunk/pygame_util.py&quot;, line 124, in draw_segment
      p1 = to_pygame(a, self.surface)
    File &quot;/home/michelangelo/miniconda3/envs/main/lib/python3.7/site-packages/pymunk/pygame_util.py&quot;, line 184, in to_pygame
      return int(p[0]), surface.get_height()-int(p[1])
  ValueError: cannot convert float NaN to integer
  </code></pre>
  <p>The error happens after the springs are apped to the space.</p>
  <p>From what I understood from the Traceback the problem is that there is a body with Vec2d(Nan,Nan) position, however I am not able to properly debug this problem.</p>
  <p>Am I doing something wrong or is it a bug in the package?
  Am I using DumpedSpring in a way it should not be used? If so, do yyou have any alternative suggestion?</p>
  <p>Thank you very much!</p>
  <p>Kind regards,
  Michelangelo</p>