advapi32/tests: Add a test to show that OpenSCManager clears last error on success.

dlls/advapi32/tests/service.c

@@ -101,7 +101,6 @@ static void test_open_scm(void)
     CloseServiceHandle(scm_handle); /* Just in case */
 
     /* Proper call with an empty hostname */
-    SetLastError(0xdeadbeef);
     scm_handle = OpenSCManagerA("", SERVICES_ACTIVE_DATABASEA, SC_MANAGER_CONNECT);
     ok(scm_handle != NULL, "Expected success, got error %u\n", GetLastError());
     CloseServiceHandle(scm_handle);
@@ -109,6 +108,7 @@ static void test_open_scm(void)
     /* Again a correct one */
     SetLastError(0xdeadbeef);
     scm_handle = OpenSCManagerA(NULL, NULL, SC_MANAGER_CONNECT);
+    ok(GetLastError() == ERROR_SUCCESS, "Expected ERROR_SUCCESS, got %u\n", GetLastError());
     ok(scm_handle != NULL, "Expected success, got error %u\n", GetLastError());
     CloseServiceHandle(scm_handle);
 }