Cargo weight modifier update (#1687)

* fixes cargo weight mod bottoming to 0 (#53812)

* Remove duplicated entry

Not truly duplicated, but the second entry provides better info and an illustration of use.

Co-authored-by: Dillon Matchett <dillon.matchett@gmail.com>

doc/JSON_INFO.md

@@ -1488,7 +1488,6 @@ Vehicle components when installed on a vehicle.
 "durability": 200,            // How much damage the part can take before breaking
 "description": "A wheel."     // A description of this vehicle part when installing it
 "size": 2000                  // If vehicle part has flag "FLUIDTANK" then capacity in mLs, else divide by 4 for volume on space
-"cargo_weight_modifier": 100  // Special function to multiplicatively modify item weight on space. Divide by 100 for ratio.
 "wheel_width": 9,             /* (Optional, default = 0)
                                * SPECIAL: A part may have at most ONE of the following fields:
                                *    wheel_width = base wheel width in inches

src/vehicle.cpp

@@ -6809,7 +6809,7 @@ void vehicle::calc_mass_center( bool use_precalc ) const
             m_part_items += j.weight();
         }
         if( vp.part().info().cargo_weight_modifier != 100 ) {
-            m_part_items *= vp.part().info().cargo_weight_modifier / 100;
+            m_part_items *= static_cast<float>( vp.part().info().cargo_weight_modifier ) / 100.0f;
         }
         m_part += m_part_items;