REG->5.13/XCB: Qt Creator crashes near QComposeInputContext::ensureInitialized() when setting LANG=de.UTF-8

Since roughly 4.3.2019, Qt Creator crashes frequently when editing text near QComposeInputContext::ensureInitialized() . I have not managed to reproduce this with a simple example.

qtbase /5.13 at 1270aeb0f96547ad32512c92ee2e69adb1f27011

qt-creator/4.9 at 26f6cbf8b59dffa7f47b315031b7055ec3421315

It might be related to "platforminputcontexts: use libxkbcommon compose key API" 2065bc070dcd1f88a1f5ba3dd6ef0139a9a441ec https://codereview.qt-project.org/#/c/98062/ .

Reverting the change seems to help at the cost of introducing warnings:

qt.xkb.compose: error: xkb context has not been set on QComposeInputContext