Fix: do not let shares in the company taking over another company disappear

src/economy.cpp

@@ -324,13 +324,13 @@ void ChangeOwnershipOfCompanyItems(Owner old_owner, Owner new_owner)
 
 		/* Sell all the shares that people have on this company */
 		Backup<CompanyID> cur_company2(_current_company, FILE_LINE);
-		const Company *c = Company::Get(old_owner);
+		Company *c = Company::Get(old_owner);
 		for (i = 0; i < 4; i++) {
 			if (c->share_owners[i] == INVALID_OWNER) continue;
 
 			if (c->bankrupt_value == 0 && c->share_owners[i] == new_owner) {
 				/* You are the one buying the company; so don't sell the shares back to you. */
-				Company::Get(new_owner)->share_owners[i] = INVALID_OWNER;
+				c->share_owners[i] = INVALID_OWNER;
 			} else {
 				cur_company2.Change(c->share_owners[i]);
 				/* Sell the shares */