dmscript/tests: Initialize test variable (valgrind) (try 2)

[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..a73f7c6 100644
--- a/dlls/dmscript/tests/dmscript.c
+++ b/dlls/dmscript/tests/dmscript.c
@@ -206,7 +206,7 @@ static void test_scripttrack(void)
 {
     IDirectMusicTrack *dmt;
     IPersistStream *ps;
-    CLSID class;
+    CLSID class = {0};
     ULARGE_INTEGER size;
     HRESULT hr;