Fixed divison by zero in the computation of a direction vector in ccd…

…MPRPenetration. (fixes #49)

In some cases, a touching contact is found in the findPenetr function. In this
case the direction vector is set to (0, 0, 0).

src/mpr.c

@@ -328,7 +328,16 @@ static void findPenetr(const void *obj1, const void *obj2, const ccd_t *ccd,
                                           &ccdSimplexPoint(portal, 3)->v,
                                           pdir);
             *depth = CCD_SQRT(*depth);
-            ccdVec3Normalize(pdir);
+            if (ccdIsZero(*depth)){
+                // If depth is zero, then we have a touching contact.
+                // So following findPenetrTouch(), we assign zero to
+                // the direction vector (it can actually be anything
+                // according to the decription of ccdMPRPenetration
+                // function).
+                ccdVec3Copy(pdir, ccd_vec3_origin);
+            }else{
+                ccdVec3Normalize(pdir);
+            }
 
             // barycentric coordinates:
             findPos(obj1, obj2, ccd, portal, pos);