similarly improve comments on Hebrew ccc 18 & 19

Should have committed this along with commit 9658435a25c2ba82 but forgot.
diff --git a/src/hb-ot-shape-fallback.cc b/src/hb-ot-shape-fallback.cc
index 7d00a35..eb1bc79 100644
--- a/src/hb-ot-shape-fallback.cc
+++ b/src/hb-ot-shape-fallback.cc
@@ -92,7 +92,7 @@
     case HB_MODIFIED_COMBINING_CLASS_CCC15: /* tsere */
     case HB_MODIFIED_COMBINING_CLASS_CCC16: /* segol */
     case HB_MODIFIED_COMBINING_CLASS_CCC17: /* patah */
-    case HB_MODIFIED_COMBINING_CLASS_CCC18: /* qamats */
+    case HB_MODIFIED_COMBINING_CLASS_CCC18: /* qamats & qamats qatan */
     case HB_MODIFIED_COMBINING_CLASS_CCC20: /* qubuts */
     case HB_MODIFIED_COMBINING_CLASS_CCC22: /* meteg */
       return HB_UNICODE_COMBINING_CLASS_BELOW;
@@ -104,7 +104,7 @@
       return HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;
 
     case HB_MODIFIED_COMBINING_CLASS_CCC25: /* sin dot */
-    case HB_MODIFIED_COMBINING_CLASS_CCC19: /* holam */
+    case HB_MODIFIED_COMBINING_CLASS_CCC19: /* holam & holam haser for vav */
       return HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT;
 
     case HB_MODIFIED_COMBINING_CLASS_CCC26: /* point varika */