opcservices: Update content stream position on Read().

dlls/opcservices/package.c

@@ -560,6 +560,8 @@ static HRESULT WINAPI opc_content_stream_Read(IStream *iface, void *buff, ULONG
     if (*num_read)
         memcpy(buff, stream->content->data + stream->pos.QuadPart, *num_read);
 
+    stream->pos.QuadPart += *num_read;
+
     return S_OK;
 }
 

dlls/opcservices/tests/opcservices.c

@@ -159,6 +159,11 @@ static void test_package(void)
     ok(hr == S_OK, "Failed to read content, hr %#x.\n", hr);
     ok(!memcmp(buff, "abc", 3), "Unexpected content.\n");
 
+    move.QuadPart = 0;
+    hr = IStream_Seek(stream2, move, STREAM_SEEK_CUR, &pos);
+    ok(SUCCEEDED(hr), "Seek failed, hr %#x.\n", hr);
+    ok(pos.QuadPart == 3, "Unexpected position.\n");
+
     IStream_Release(stream);
     IStream_Release(stream2);