Refine handling of container state synchronisation

When a container is closed, the outer container's buffer state is
synchronised with the inner container's state.

This was previously done via:

```
CborError cbor_encoder_close_container(CborEncoder *encoder, const CborEncoder *containerEncoder)
{
    if (encoder->end)
        encoder->data.ptr = containerEncoder->data.ptr;
    else
        encoder->data.bytes_needed = containerEncoder->data.bytes_needed;
    encoder->end = containerEncoder->end;

    ...

    return CborNoError;
}
```

However, strictly speaking the inner container could have updated `end` to be `NULL` if
the buffer was too small. In that case, the outer container should carry over `bytes_needed`
and not `ptr`. However, the logic was using the outer container's "stale" view of `end`.

However, generally `sizeof(ptr)` and `sizeof(bytes_needed)` are the same, and these values
exist in a union. Therefore, the correct values where still being copied.

This change moves the synchronisation of `end` to ahead of the synchronisation of `data`.

It additionally, actually avoids this potential error by simply synchronising the full `data`
structure, thereby avoiding the conditional logic. Simplifying the code to simply:

```
encoder->end = containerEncoder->end;
encoder->data = containerEncoder->data;
```

Author: sgebbie

src/cborencoder.c

@@ -540,11 +540,10 @@ CborError cbor_encoder_create_map(CborEncoder *encoder, CborEncoder *mapEncoder,
  */
 CborError cbor_encoder_close_container(CborEncoder *encoder, const CborEncoder *containerEncoder)
 {
-    if (encoder->end)
-        encoder->data.ptr = containerEncoder->data.ptr;
-    else
-        encoder->data.bytes_needed = containerEncoder->data.bytes_needed;
+    // synchronise buffer state with that of the container
     encoder->end = containerEncoder->end;
+    encoder->data = containerEncoder->data;
+
     if (containerEncoder->flags & CborIteratorFlag_UnknownLength)
         return append_byte_to_buffer(encoder, BreakByte);
 
@@ -553,6 +552,7 @@ CborError cbor_encoder_close_container(CborEncoder *encoder, const CborEncoder *
 
     if (!encoder->end)
         return CborErrorOutOfMemory;    /* keep the state */
+
     return CborNoError;
 }