Fix a few bugs.

- Moving lines after themselves didnt work.
- moving empty lines deleted them.
- "w" didnt set state to unmodified in generic buffers.
- in "hl" aligned the numbers (by digits)

src/internal/vase/vase.cc

@@ -182,8 +182,6 @@ Shard *insert(AppendStorage *ap, Shard *root, Shard *text, uint64_t line) {
     Shard::retain(text);
     return text;
   }
-  if (!text)
-    return root;
   if (line > root->lines + 1)
     throw ed_error("line out of range");
   Shard::retain(text);