[QJson] Hack to check for Indent support

There is no library version available in header files, so this is
the only solution to fix building on Debian stable

src/defines.pri

@@ -58,6 +58,9 @@ else {
     }
 }
 
+# Ugly hack to check for Indent support in QJson
+system(grep "enum IndentMode" /usr/include/qjson/serializer.h &> /dev/null): DEFINES *= QJSON_HAVE_INDENT
+
 DEFINES *= QT_NO_URL_CAST_FROM_STRING
 DEFINES *= QT_USE_QSTRINGBUILDER
 

src/lib/tools/json.cpp

@@ -45,8 +45,16 @@ QByteArray Json::serialize(const QVariant &variant, bool* ok)
 {
 #if QT_VERSION < 0x050000
     QJson::Serializer serializer;
+#ifdef QJSON_HAVE_INDENT
     serializer.setIndentMode(QJson::IndentFull);
-    return serializer.serialize(variant, ok);
+#endif
+    const QByteArray data = serializer.serialize(variant);
+
+    if (ok) {
+        *ok = !data.isNull();
+    }
+
+    return data;
 #else
     QJsonDocument doc = QJsonDocument::fromVariant(variant);