Patch 37a1fd88: Sync selectedChannel only if the channel doesn't exist

## Issue
The previous commit was over-doing the manual syncing, causing other usages like the Repost Modal to always reset to a different channel.

## Fix
Only do the manual syncing when the channel does not exist.
At this point, we could also just take `channel[0]` as the new value.

ui/component/selectChannel/view.jsx

@@ -47,6 +47,7 @@ class ChannelSelection extends React.PureComponent<Props, State> {
       fetchChannelListMine();
     }
 
+    if (channels && channels.length && !channels.find(chan => chan.name === channel)) {
       const elem = document.getElementById(ID_FF_SELECT_CHANNEL);
       // $FlowFixMe
       if (elem && elem.value && elem.value !== channel) {
@@ -56,6 +57,7 @@ class ChannelSelection extends React.PureComponent<Props, State> {
         }, 250);
       }
     }
+  }
 
   componentDidUpdate() {
     const { channels, fetchingChannels, hideAnon } = this.props;