Memory Viewer: Improve display of NdArrays, fix passing -1 as num rows/cols

source/RobotAPI/libraries/armem_gui/instance/display_visitors/DataDisplayVisitor.h

@@ -4,20 +4,18 @@
 
 #include <RobotAPI/libraries/aron/core/data/visitor/variant/VariantVisitor.h>
 
+#include "StringStreamMixin.h"
 
 namespace armarx::aron
 {
 
-    class DataDisplayVisitor : public aron::data::ConstVariantVisitor
+    class DataDisplayVisitor : public aron::data::ConstVariantVisitor, public StringStreamMixin
     {
     public:
         static std::string getValue(const data::VariantPtr& n);
 
 
     public:
-
-        std::stringstream value;
-
         void visitDict(const data::VariantPtr& n) override;
         void visitList(const data::VariantPtr& n) override;
 
@@ -29,7 +27,6 @@ namespace armarx::aron
         void visitString(const data::VariantPtr& n) override;
 
         void visitNDArray(const data::VariantPtr& n) override;
-
     };
 
-}
+} // namespace armarx::aron