[IE TESTS] Incorrect calculation for 'Convert' number of test crashes (#5922)

* Hiding the problem, but not solving it, Validate() changes the value of a variable function

* [IE TESTS] Convert issue

* [IE TESTS] Solving the problem of adding an extra layer

inference-engine/tests/functional/plugin/shared/include/behavior/preprocessing.hpp

@@ -110,9 +110,12 @@ public:
     }
 
     void Validate() override {
+        // w/a: copy of original function is required to provide correct op coverage report (overflow of convert counter issue)
+        auto copyOriginalFunction = function;
         //force the reference implementation to use graph with extra Convert operation
         function = reference_function;
         LayerTestsUtils::LayerTestsCommon::Validate();
+        function = copyOriginalFunction;
     }
 
 public: