antihacks: Protect per-player detached inventory actions

* backported https://github.com/minetest/minetest/pull/10341
  Unfortunately also requires invhack mods to implement workarounds,
  but they seem to already be doing this.

lib/lua/src/loadlib.c

@@ -73,7 +73,7 @@ static void *ll_load (lua_State *L, const char *path) {
 
 
 static lua_CFunction ll_sym (lua_State *L, void *lib, const char *sym) {
-  lua_CFunction f = (lua_CFunction)dlsym(lib, sym);
+  lua_CFunction f = __extension__(lua_CFunction)dlsym(lib, sym);
   if (f == NULL) lua_pushstring(L, dlerror());
   return f;
 }

src/network/serverpackethandler.cpp

@@ -935,13 +935,19 @@ void Server::handleCommand_InventoryAction(NetworkPacket* pkt)
 		setInventoryModified(ma->from_inv, false);
 		setInventoryModified(ma->to_inv, false);
 
-		bool from_inv_is_current_player =
+		bool from_inv_is_current_player = false;
-			(ma->from_inv.type == InventoryLocation::PLAYER) &&
+		if (ma->from_inv.type == InventoryLocation::PLAYER) {
-			(ma->from_inv.name == player->getName());
+			if (ma->from_inv.name != player->getName())
+				return;
+			from_inv_is_current_player = true;
+		}
 
-		bool to_inv_is_current_player =
+		bool to_inv_is_current_player = false;
-			(ma->to_inv.type == InventoryLocation::PLAYER) &&
+		if (ma->to_inv.type == InventoryLocation::PLAYER) {
-			(ma->to_inv.name == player->getName());
+			if (ma->to_inv.name != player->getName())
+				return;
+			to_inv_is_current_player = true;
+		}
 
 		InventoryLocation *remote = from_inv_is_current_player ?
 			&ma->to_inv : &ma->from_inv;