Windows: simplify WMI query code

by making C++ code more C++

src/detection/cpuUsage/cpuUsage_nowait_windows.cpp

@@ -5,22 +5,14 @@ extern "C" {
 
 extern "C" const char* ffGetCpuUsageResultNoWait(double* result)
 {
-    IEnumWbemClassObject* pEnumerator = ffQueryWmi(L"SELECT LoadPercentage FROM Win32_Processor", nullptr);
-    if(!pEnumerator)
+    FFWmiQuery query(L"SELECT LoadPercentage FROM Win32_Processor");
+    if(!query)
         return "Query WMI service failed";
 
-    IWbemClassObject *pclsObj = NULL;
-    ULONG uReturn = 0;
-
-    if(FAILED(pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn)) || uReturn == 0)
-    {
-        pEnumerator->Release();
+    if(FFWmiRecord record = query.next())
+        record.getReal(L"LoadPercentage", result);
+    else
         return "No WMI result returned";
-    }
 
-    ffGetWmiObjReal(pclsObj, L"LoadPercentage", result);
-
-    pclsObj->Release();
-    pEnumerator->Release();
-    return NULL;
+    return nullptr;
 }