Bugfix: Show correct bodypart in grabs

Updates the message `The fat zombie grabs your right arm` so that the bodypart
being used is the same bodypart that is used for the actual grab effect.
Before, there could be cases where the message displayed a different bodypart
than what was actually grabbed since `bp_id` might be changed by the call to
`target->block_hit` after `do_grab` had completed.

src/mattack_actors.cpp

@@ -745,6 +745,7 @@ bool melee_actor::call( monster &z ) const
 
     // We need to do some calculations in the main function - we might mutate bp_hit
     // But first we need to handle exclusive grabs etc.
+    std::optional<bodypart_id> grabbed_bp_id;
     if( is_grab ) {
         int eff_grab_strength = grab_data.grab_strength == -1 ? z.get_grab_strength() :
                                 grab_data.grab_strength;
@@ -831,6 +832,7 @@ bool melee_actor::call( monster &z ) const
         } else if( result == 0 ) {
             return true;
         }
+        grabbed_bp_id = bp_id;
     }
 
     // Damage instance calculation
@@ -870,7 +872,7 @@ bool melee_actor::call( monster &z ) const
                                  sfx::get_heard_angle( z.pos() ) );
         target->add_msg_player_or_npc( msg_type, no_dmg_msg_u,
                                        get_option<bool>( "LOG_MONSTER_ATTACK_MONSTER" ) ? no_dmg_msg_npc : to_translation( "" ),
-                                       mon_name, body_part_name_accusative( bp_id ) );
+                                       mon_name, body_part_name_accusative( grabbed_bp_id.value_or( bp_id ) ) );
         if( !effects_require_dmg ) {
             for( const mon_effect_data &eff : effects ) {
                 if( x_in_y( eff.chance, 100 ) ) {