add null-guard for Autocomplete containerRef

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/rooms/Autocomplete.tsx

@@ -260,7 +260,7 @@ export default class Autocomplete extends React.PureComponent<IProps, IState> {
                 behavior: "auto",
                 block: "nearest",
             });
-        } else {
+        } else if (this.containerRef.current) {
             this.containerRef.current.scrollTo({ top: 0 });
         }
     }