Codechange: Be consistent with how company masks are set to all.

src/saveload/engine_sl.cpp

@@ -110,7 +110,7 @@ struct ENGNChunkHandler : ChunkHandler {
 				 * Just cancel any previews. */
 				e->flags &= ~4; // ENGINE_OFFER_WINDOW_OPEN
 				e->preview_company = INVALID_COMPANY;
-				e->preview_asked = (CompanyMask)-1;
+				e->preview_asked = MAX_UVALUE(CompanyMask);
 			}
 		}
 	}