[ot_shape] Sync propagate_flags with hb (harfRuzz PR #61)

Not sure why this block was not ported before.

Author: behdad

src/hb/ot_shape.rs

@@ -972,5 +972,9 @@ fn propagate_flags(buffer: &mut hb_buffer_t) {
                 info.mask = mask;
             }
         }
+
+        for info in &mut buffer.info[start..end] {
+            info.mask = mask;
+        }
     });
 }