Git: Replace subsequent invalid characters with a single underscore

... in the Add Branch dialog.

Change-Id: I7644cba6bf58316431e2daa9db5d2c26823c2711
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/branchadddialog.cpp

@@ -50,7 +50,7 @@ class BranchNameValidator : public QValidator
 public:
     BranchNameValidator(const QStringList &localBranches, QObject *parent = nullptr) :
         QValidator(parent),
-        m_invalidChars(GitPlugin::invalidBranchAndRemoteNamePattern()),
+        m_invalidChars('(' + GitPlugin::invalidBranchAndRemoteNamePattern() + ")+"),
         m_localBranches(localBranches)
     {
     }