[lib] fix changing thread description on native for thick threads

Summary:
[ENG-9316](https://linear.app/comm/issue/ENG-9316/its-not-possible-to-change-description-on-native).

The `description` is a nullable field ([link](https://github.com/CommE2E/comm/blob/d25e29a0be1e70953f0c6b34808a66438661905a/lib/types/minimally-encoded-thread-permissions-types.js#L266)), so whenever clicking editing button for not edited or not set description [here](https://github.com/CommE2E/comm/blob/3909f7edd16fdc159bf558515ee538b9dcf8deaa/native/chat/settings/thread-settings-description.react.js#L231) it causes changing value from `undefined` to `undefined` and a result nothing changes. We're not entering [this](https://github.com/CommE2E/comm/blob/3909f7edd16fdc159bf558515ee538b9dcf8deaa/native/chat/settings/thread-settings-description.react.js#L115-L148) branch which renders `TextInput`.

For thin threads, it works only because for some reason keyserver is replacing `undefined` description with an empty string [here](https://github.com/CommE2E/comm/blob/5c7f994b92c1042dd057a8453362ea9437a4c945/keyserver/src/fetchers/thread-fetchers.js#L148).

The alternative solution is to create a thick thread with an empty string as a description (instead of `undefined`), but I don't like this because types still allow for descryption to be nullable so this bug might be caused again in the future.

Test Plan:
1. Change thread settings on native works for thin and thick threads.
2. Notifs works.
3. Changing the description to the same value is a no-op.

Reviewers: tomek, ashoat

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D13447

lib/shared/dm-ops/create-thread-spec.js

@@ -119,7 +119,7 @@ function createThickRawThreadInfo(
     repliesCount: repliesCount ?? 0,
     name,
     avatar,
-    description,
+    description: description ?? '',
     containingThreadID,
     timestamps,
   };

native/chat/settings/thread-settings-description.react.js

@@ -228,7 +228,7 @@ class ThreadSettingsDescription extends React.PureComponent<Props> {
   };
 
   onPressEdit = () => {
-    this.props.setDescriptionEditValue(this.props.threadInfo.description);
+    this.props.setDescriptionEditValue(this.props.threadInfo.description ?? '');
   };
 
   onSubmit = () => {