init-repository cannot clone revisions from deleted release branches

1. git clone git://code.qt.io/qt/qt5.git
2. cd qt5
3. git checkout v5.5.1
4. perl init-repository
   This will fail:

   Cloning into 'qt3d'...
   fatal: Remote branch 5.5.1 not found in upstream origin
   git clone --branch 5.5.1 git://code.qt.io/qt/qt3d.git qt3d exited with status 32768 at init-repository line 221.
   	Qt::InitRepository::exe('Qt::InitRepository=HASH(0x20dd80)', 'git', 'clone', '--branch', 5.5.1, 'git://code.qt.io/qt/qt3d.git', 'qt3d') called at init-repository line 472
   	Qt::InitRepository::git_clone_one_submodule('Qt::InitRepository=HASH(0x20dd80)', 'qt3d', 'qt/qt3d.git', 5.5.1) called at init-repository line 378
   	Qt::InitRepository::git_clone_all_submodules('Qt::InitRepository=HASH(0x20dd80)', 'qt/qt5', 0, 'default') called at init-repository line 565
   	Qt::InitRepository::run('Qt::InitRepository=HASH(0x20dd80)') called at init-repository line 576
   

init-repository should be able to clone every released version of Qt.