[REG 3.3->3.4] Untracked files not in project are not filtered in submit editor

• Create some files that are not in the project
• Modify a file that is part of the project
• Git Commit - unrelated files are filtered out
• Switch window and switch back - unrelated files appear

VcsBaseSubmitEditor::filterUntrackedFilesOfProject() is used to find untracked files that are part of the project, in order to filter out the rest of them.

This function uses VcsBaseSubmitEditor::currentProjectFiles(), which gets the current project by calling ProjectExplorer::ProjectTree::currentProject().

When the submit editor is open, currentProject() returns 0, so no files are filtered out.