Crash in BraveNewsUtils

[SergeyZhukovsky]

I found that crash on GPC on nightly 1.68.22. It's fine to make the fix in master only as not a lot of them.
Note: there are several locations where we access mChannelList. Let's make check in all of them.

Exception java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.List.iterator()' on a null object reference
  at org.chromium.chrome.browser.brave_news.BraveNewsUtils.searchChannel (BraveNewsUtils.java:263)
  at org.chromium.chrome.browser.settings.BraveNewsPreferencesDetails.search (BraveNewsPreferencesDetails.java:269)
  at org.chromium.chrome.browser.settings.BraveNewsPreferencesDetails.lambda$onCreateOptionsMenu$7 (BraveNewsPreferencesDetails.java:258)
  at org.chromium.components.browser_ui.settings.SearchUtils$1.onQueryTextChange (SearchUtils.java:97)
  at androidx.appcompat.widget.SearchView.onTextChanged (SearchView.java:1198)
  at androidx.appcompat.widget.SearchView$10.onTextChanged (SearchView.java:1736)
  at android.widget.TextView.sendOnTextChanged (TextView.java:10588)
  at android.widget.TextView.handleTextChanged (TextView.java:10695)
  at android.widget.TextView$ChangeWatcher.onTextChanged (TextView.java:13578)
  at android.text.SpannableStringBuilder.sendTextChanged (SpannableStringBuilder.java:1267)
  at android.text.SpannableStringBuilder.replace (SpannableStringBuilder.java:576)
  at androidx.emoji2.text.SpannableBuilder.replace (SpannableBuilder.java:308)
  at android.text.SpannableStringBuilder.replace (SpannableStringBuilder.java:507)
  at androidx.emoji2.text.SpannableBuilder.replace (SpannableBuilder.java:298)
  at androidx.emoji2.text.SpannableBuilder.replace (SpannableBuilder.java:48)
  at android.view.inputmethod.BaseInputConnection.replaceText (BaseInputConnection.java:861)
  at android.view.inputmethod.BaseInputConnection.setComposingText (BaseInputConnection.java:633)
  at android.view.inputmethod.InputConnectionWrapper.setComposingText (InputConnectionWrapper.java:142)
  at com.android.internal.view.IInputConnectionWrapper.executeMessage (IInputConnectionWrapper.java:399)
  at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage (IInputConnectionWrapper.java:93)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loop (Looper.java:236)
  at android.app.ActivityThread.main (ActivityThread.java:8107)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:656)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:967)