Fixed|Server|libcommon: Player's weapon was undefined after map change

Now the player's ready weapon is always updated after the map changes
and the players are respawned. The bug occurred at least in Heretic.

doomsday/plugins/common/src/p_start.c

@@ -581,6 +581,8 @@ void P_SpawnPlayer(int plrNum, playerclass_t pClass, coord_t x, coord_t y, coord
 
     p->brain.changeWeapon = WT_NOCHANGE;
 
+    p->update |= PSF_READY_WEAPON | PSF_PENDING_WEAPON;
+
     // Setup gun psprite.
     P_SetupPsprites(p);