msi: An empty string is equivalent to nil, so handle this in the optimised WHERE_execute path.

dlls/msi/where.c

@@ -265,12 +265,18 @@ static UINT WHERE_execute( struct tagMSIVIEW *view, MSIRECORD *record )
         if ((col_cond->type == EXPR_COL_NUMBER_STRING) && (val_cond->type == EXPR_SVAL))
         {
             col = col_cond->u.col_number;
+            /* special case for "" - translate it into nil */
+            if (!val_cond->u.sval[0])
+                value = 0;
+            else
+            {
                 r = msi_string2idW(wv->db->strings, val_cond->u.sval, &value);
                 if (r != ERROR_SUCCESS)
                 {
                     TRACE("no id for %s, assuming it doesn't exist in the table\n", debugstr_w(wv->cond->u.expr.right->u.sval));
                     return ERROR_SUCCESS;
                 }
+            }
 
             do
             {