pdh/tests: Add test for size > 0 but no buffer.

dlls/pdh/tests/pdh.c

@@ -646,6 +646,10 @@ static void test_PdhLookupPerfNameByIndexA( void )
     ok(size == sizeof("% Processor Time"), "PdhLookupPerfNameByIndexA failed %d\n", size);
 
     size = sizeof(buffer);
+    ret = PdhLookupPerfNameByIndexA( NULL, 674, NULL, &size );
+    ok(ret == PDH_INVALID_ARGUMENT, "PdhLookupPerfNameByIndexA failed 0x%08x\n", ret);
+
+    size = sizeof(buffer);
     ret = PdhLookupPerfNameByIndexA( NULL, 674, buffer, &size );
     ok(ret == ERROR_SUCCESS, "PdhLookupPerfNameByIndexA failed 0x%08x\n", ret);
     ok(!lstrcmpA( buffer, "System Up Time" ),
@@ -672,6 +676,10 @@ static void test_PdhLookupPerfNameByIndexW( void )
     ok(size == sizeof(processor_time) / sizeof(WCHAR), "PdhLookupPerfNameByIndexW failed %d\n", size);
 
     size = sizeof(buffer) / sizeof(WCHAR);
+    ret = PdhLookupPerfNameByIndexW( NULL, 674, NULL, &size );
+    ok(ret == PDH_INVALID_ARGUMENT, "PdhLookupPerfNameByIndexW failed 0x%08x\n", ret);
+
+    size = sizeof(buffer) / sizeof(WCHAR);
     ret = PdhLookupPerfNameByIndexW( NULL, 674, buffer, &size );
     ok(ret == ERROR_SUCCESS, "PdhLookupPerfNameByIndexW failed 0x%08x\n", ret);
     ok(size == sizeof(uptime) / sizeof(WCHAR), "PdhLookupPerfNameByIndexW failed %d\n", size);