some riffs on PR #806 (#1163)

In ship::clear(), The E removed

memset(&weapons, 0, sizeof(ship_weapon));

but did not add a corresponding

weapons = ship_weapon();

This fixes that.  Additionally, this PR removes one of the two uses of ship::clear() by tweaking hud_observer_init.  Originally, the code used memcpy, but if the assignment operator works for ai_info, it should be suitable for ship too.

Author: Goober5000

code/ship/ship.cpp

@@ -5821,6 +5821,8 @@ void ship::clear()
 	target_shields_delta = 0.0f;
 	target_weapon_energy_delta = 0.0f;
 
+	weapons = ship_weapon();
+
 	// ---------- special weapons init that isn't setting things to 0
 	for (i = 0; i < MAX_SHIP_PRIMARY_BANKS; i++)
 	{