Properly propagate pack usage to UI

We can't have a pack that is neither sticker nor emoji. Which is why
none defaults to both on. That wasn't propagated to the UI, which made
the interaction very confusing. It also made some states unsettable,
since you can't turn anything off from the none state.

fixes #1152

src/SingleImagePackModel.cpp

@@ -248,6 +248,9 @@ SingleImagePackModel::setIsStickerPack(bool val)
     using mtx::events::msc2545::PackUsage;
     if (val != pack.pack->is_sticker()) {
         pack.pack->usage.set(PackUsage::Sticker, val);
+        if (!val)
+            pack.pack->usage.set(PackUsage::Emoji, true);
+        emit isEmotePackChanged();
         emit isStickerPackChanged();
     }
 }
@@ -258,7 +261,10 @@ SingleImagePackModel::setIsEmotePack(bool val)
     using mtx::events::msc2545::PackUsage;
     if (val != pack.pack->is_emoji()) {
         pack.pack->usage.set(PackUsage::Emoji, val);
+        if (!val)
+            pack.pack->usage.set(PackUsage::Sticker, true);
         emit isEmotePackChanged();
+        emit isStickerPackChanged();
     }
 }