fix(tests): remove a possible memleak from tests

Signed-off-by: Andrea Terzolo <[email protected]>

userspace/libsinsp/test/sinsp_with_test_input.h

@@ -411,7 +411,17 @@ class sinsp_with_test_input : public ::testing::Test {
 			throw sinsp_exception("The event class is NULL");
 		}
 
-		return flist.new_filter_check_from_fldname(field_name, &m_inspector, false) != nullptr;
+		auto new_fl = flist.new_filter_check_from_fldname(field_name, &m_inspector, false);
+		if(new_fl != nullptr)
+		{
+			// if can create a filter check it means that the field exists
+			delete new_fl;
+			return true;
+		}
+		else
+		{
+			return false;
+		}
 	}
 
 	// Return true if `field_name` value is not NULL for this event.