Remove explicit instantiation of customReactionName variable and add types

Co-authored-by: Šimon Brandner <simon.bra.ag@gmail.com>

Author: sumnerevans

src/components/views/messages/ReactionsRowButton.tsx

@@ -107,7 +107,7 @@ export default class ReactionsRowButton extends React.PureComponent<IProps, ISta
 
         const room = this.context.getRoom(mxEvent.getRoomId());
         let label: string | undefined;
-        let customReactionName = "";
+        let customReactionName: string | undefined;
         if (room) {
             const senders: string[] = [];
             for (const reactionEvent of reactionEvents) {

src/components/views/messages/ReactionsRowButtonTooltip.tsx

@@ -43,7 +43,7 @@ export default class ReactionsRowButtonTooltip extends React.PureComponent<IProp
         let tooltipLabel: JSX.Element | undefined;
         if (room) {
             const senders: string[] = [];
-            let customReactionName = "";
+            let customReactionName: string | undefined;
             for (const reactionEvent of reactionEvents) {
                 const member = room.getMember(reactionEvent.getSender()!);
                 const name = member?.name ?? reactionEvent.getSender()!;