[kern/kerx] Fix cursive joining

Tested with Waseem TTC:

$ hb-shape Waseem.ttc جحخج
[F1Jeem_R2=3@0,180+479|M1Khah_L2_R2=2@0,682+403|M1Hah_L2_R2=1@0,1184+403|I1Jeem_L2=0@0,1184+744]

src/hb-aat-layout-kerx-table.hh

@@ -284,6 +284,8 @@ struct KerxSubTableFormat1
 	}
 	depth = 0;
       }
+      else
+	buffer->pos[buffer->idx].y_offset += c->font->em_scale_y (crossOffset);
 
       return true;
     }

src/hb-ot-kern-table.hh

@@ -334,6 +334,8 @@ struct KernSubTableFormat1
 	}
 	depth = 0;
       }
+      else
+	buffer->pos[buffer->idx].y_offset += c->font->em_scale_y (crossOffset);
 
       return true;
     }