[ttgxvar] Fix crash in COLRv1.

This is a stopgap until issue #1202 is properly fixed.

* src/truetype/ttxgvar.c (tt_var_get_item_delta): Check `normalizedcoords`.

src/truetype/ttgxvar.c

@@ -1009,6 +1009,9 @@
     FT_ItemVarDelta   returnValue;
 
 
+    if ( !face->blend->normalizedcoords )
+      return 0;
+
     /* OpenType 1.8.4+: No variation data for this item
      *  as indices have special value 0xFFFF. */
     if ( outerIndex == 0xFFFF && innerIndex == 0xFFFF )