compose: On recent servers, quote-and-reply doesn't fill empty topic input

[chrisbobbe]

To reproduce:

1. Connect to CZO or another realm with feature level 334+
2. Enter a channel narrow
3. Long-press a message; tap "Quote and reply"
4. See the content input update with the quoted message

Expected: the topic input is automatically filled with the message's topic

Actual: the topic input remains blank

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This looks like a regression from the recent "general chat" work. To check if the topic input was left empty, the quote-and-reply button checks the condition composeBoxController.topic.textNormalized == kNoTopicTopic. Before 769cc7d, that condition was a reliable test of whether the topic input was left empty. But it isn't reliable anymore; on recent servers, if the topic input is left empty, composeBoxController.topic.textNormalized will be the empty string.

Assigning @PIG208 as the author of 769cc7d.