Vcs: Initializing of the VcsEditorWidgets crashes QC on OSX

Steps to reproduce:

• start QC, open a repository
• invoke 'git log' inside the Locator

OR

• run one of the Plugin Unit tests of QC related to Vcs (Bazaar, CVS, Git, Perforce, Mercurial, Subversion)

Note: I could reproduce this only using a self-compiled QC using Qt5.3.2, this wasn't reproducable using the QC3.3 beta snapshots based on Qt5.4.