fix scope of ship arc sound generation

The code for generating spark sounds was incorrectly copied from debris to ships, dating all the way back to retail.  The sound should be played once per generation event, not once for every electrical arc active on the ship.  This fixes a bug that caused overlapping electrical arc sounds.

Author: Goober5000

code/debris/debris.cpp

@@ -302,14 +302,13 @@ void debris_process_post(object * obj, float frame_time)
 						arc->endpoint_1 = v2;
 						arc->endpoint_2 = v3;
 						break;
-
 					case 2:
 						arc->endpoint_1 = v2;
 						arc->endpoint_2 = v4;
 						break;
 
 					default:
-						Int3();
+						UNREACHABLE("Unhandled case %d for electrical arc creation in debris_process_post()!", n);
 					}
 
 					n++;

code/ship/shipfx.cpp

@@ -2220,14 +2220,13 @@ void shipfx_do_lightning_arcs_frame( ship *shipp )
 					arc->endpoint_1 = v2;
 					arc->endpoint_2 = v3;
 					break;
-
 				case 2:
 					arc->endpoint_1 = v2;
 					arc->endpoint_2 = v4;
 					break;
 
 				default:
-					Int3();
+					UNREACHABLE("Unhandled case %d for electrical arc creation in shipfx_do_lightning_arcs_frame()!", n);
 				}
 
 				// determine what kind of arc to create
@@ -2244,30 +2243,30 @@ void shipfx_do_lightning_arcs_frame( ship *shipp )
 			} else if (arc->type == MARC_TYPE_DAMAGED || arc->type == MARC_TYPE_EMP) {
 				num_damage_arcs ++;
 			}
+		}
 
-			// rotate v2 out of local coordinates into world.
-			// Use v2 since it is used in every bolt.  See above switch().
-			vec3d snd_pos;
-			vm_vec_unrotate(&snd_pos, &v2, &obj->orient);
-			vm_vec_add2(&snd_pos, &obj->pos );
-
-			//Play a sound effect
-			if ( lifetime > 750 )	{
-				// 1.00 second effect
-				snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_05), &snd_pos, &View_position, obj->radius );
-			} else if ( lifetime >  500 )	{
-				// 0.75 second effect
-				snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_04), &snd_pos, &View_position, obj->radius );
-			} else if ( lifetime >  250 )	{
-				// 0.50 second effect
-				snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_03), &snd_pos, &View_position, obj->radius );
-			} else if ( lifetime >  100 )	{
-				// 0.25 second effect
-				snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_02), &snd_pos, &View_position, obj->radius );
-			} else {
-				// 0.10 second effect
-				snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_01), &snd_pos, &View_position, obj->radius );
-			}
+		// rotate v2 out of local coordinates into world.
+		// Use v2 since it is used in every bolt.  See above switch().
+		vec3d snd_pos;
+		vm_vec_unrotate(&snd_pos, &v2, &obj->orient);
+		vm_vec_add2(&snd_pos, &obj->pos );
+
+		//Play a sound effect
+		if ( lifetime > 750 )	{
+			// 1.00 second effect
+			snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_05), &snd_pos, &View_position, obj->radius );
+		} else if ( lifetime >  500 )	{
+			// 0.75 second effect
+			snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_04), &snd_pos, &View_position, obj->radius );
+		} else if ( lifetime >  250 )	{
+			// 0.50 second effect
+			snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_03), &snd_pos, &View_position, obj->radius );
+		} else if ( lifetime >  100 )	{
+			// 0.25 second effect
+			snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_02), &snd_pos, &View_position, obj->radius );
+		} else {
+			// 0.10 second effect
+			snd_play_3d( gamesnd_get_game_sound(GameSounds::DEBRIS_ARC_01), &snd_pos, &View_position, obj->radius );
 		}
 	}