CPatch: change default preallocated size to 12 instead of 6

This has the effect of setting the base `max_size` of a ContactPatchRequest
to 12 instead of 6.
This is to make sure the box-box case is fully captured.

Author: lmontaut

include/hpp/fcl/collision_data.h

@@ -545,7 +545,7 @@ struct HPP_FCL_DLLAPI ContactPatch {
 
   /// @brief Default maximum size of the polygon representing the set.
   /// Used to pre-allocate memory for the patch.
-  static constexpr size_t default_preallocated_size = 6;
+  static constexpr size_t default_preallocated_size = 12;
 
  protected:
   /// @brief Container for the vertices of the set.