Git BranchAddDialog: fix branch renaming

replace invalid characters with '_'. To allow pasting of text with
invalid chars inside

Change-Id: Ibc0d3dde2252235a931b51ad73ae2eef527be547
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/branchadddialog.cpp

@@ -70,11 +70,7 @@ public:
     {
         Q_UNUSED(pos)
 
-        // NoGos
-
-        if (input.contains(m_invalidChars))
-            return Invalid;
-
+        input.replace(m_invalidChars, QLatin1String("_"));
 
         // "Intermediate" patterns, may change to Acceptable when user edits further: