ProjectSummaryPage: Report no VersionControl as ""

Returning QString() from here for unset vc will result in the
substitution to fail and thus will leave "%{VersionControl}" as
the text.

Returning a empty non-Null string will make turn the replacement
into "" instead, which is what is expected.

Change-Id: I9dc890deb5f9ea1ac28c1546e4c1bce804d196ef
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/plugins/projectexplorer/jsonwizard/jsonsummarypage.cpp

@@ -197,7 +197,7 @@ void JsonSummaryPage::projectNodeHasChanged()
 void JsonSummaryPage::versionControlHasChanged()
 {
     IVersionControl *vc = currentVersionControl();
-    m_wizard->setProperty("VersionControl", vc ? vc->id().toString() : QString());
+    m_wizard->setProperty("VersionControl", vc ? vc->id().toString() : QLatin1String(""));
 
     updateFileList();
 }