Don't access static functions/fields via instance

Courtesy of readability-static-accessed-through-instance

Amends: b2a766a79a

Round #2: This time done with Qt Creator's Analyzer, which
found other occurences than run-clang-tidy.py

Change-Id: I479e280c7abcf2d24baccbb0af69ae4bda05198e
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/git/logchangedialog.cpp

@@ -106,10 +106,8 @@ bool LogChangeWidget::init(const QString &repository, const QString &commit, Log
         return false;
     if (m_model->rowCount() > 0)
         return true;
-    if (!(flags & Silent)) {
-        VcsOutputWindow::appendError(
-                    GitClient::instance()->msgNoCommits(flags & IncludeRemotes));
-    }
+    if (!(flags & Silent))
+        VcsOutputWindow::appendError(GitClient::msgNoCommits(flags & IncludeRemotes));
     return false;
 }