Update qtabbar.cpp

[itree13]

fix: text disappeared when moving

[ChungZH]

Don't PR in GitHub.

[jonaski]

Qt doesn't use GitHub, this needs to be submitted to Gerrit codereview (https://codereview.qt-project.org/). For instructions see: https://wiki.qt.io/Setting_up_Gerrit and https://wiki.qt.io/Gerrit_Introduction

[cla-assistant]

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