dmscript/tests: Initialize test variable (valgrind)

[Bruno Jesus]

Fixes bug https://bugs.winehq.org/show_bug.cgi?id=36809
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diff --git a/dlls/dmscript/tests/dmscript.c b/dlls/dmscript/tests/dmscript.c
index 02fddc3..6b9a6ac 100644
--- a/dlls/dmscript/tests/dmscript.c
+++ b/dlls/dmscript/tests/dmscript.c
@@ -209,6 +209,7 @@ static void test_scripttrack(void)
     CLSID class;
     ULARGE_INTEGER size;
     HRESULT hr;
+    memset(&class, 0, sizeof(CLSID));
 
     hr = CoCreateInstance(&CLSID_DirectMusicScriptTrack, NULL, CLSCTX_INPROC_SERVER,
             &IID_IDirectMusicTrack, (void**)&dmt);