jscript: Use jsstr_flatten to access string buffer in jsutils.c.

dlls/jscript/jsutils.c

@@ -502,16 +502,15 @@ static int hex_to_int(WCHAR c)
 /* ECMA-262 3rd Edition    9.3.1 */
 static HRESULT str_to_number(jsstr_t *str, double *ret)
 {
-    const WCHAR *ptr = str->str;
+    const WCHAR *ptr;
     BOOL neg = FALSE;
     DOUBLE d = 0.0;
 
     static const WCHAR infinityW[] = {'I','n','f','i','n','i','t','y'};
 
-    if(!ptr) {
-        *ret = 0;
-        return S_OK;
-    }
+    ptr = jsstr_flatten(str);
+    if(!ptr)
+        return E_OUTOFMEMORY;
 
     while(isspaceW(*ptr))
         ptr++;