Uncaught TypeError: Cannot read property 'name' of undefined

Seems like a re-occurance of #16

1. Open file with no headers in tablr
2. Edit header name of one column

**Atom**: 1.14.4 x64
**Electron**: 1.3.13
**OS**: Mac OS X 10.12.3
**Thrown From**: [tablr](https://github.com/abe33/atom-tablr) package 1.8.1

### Stack Trace

Uncaught TypeError: Cannot read property 'name' of undefined

```
At /Users/lparsons/.atom/packages/tablr/lib/table-element.js:1344

TypeError: Cannot read property 'name' of undefined
at /packages/tablr/lib/table-element.js:1344:49)
at /packages/tablr/lib/table-element.js:1414:14)
at /packages/tablr/lib/table-element.js:30:17)
at CommandRegistry.module.exports.CommandRegistry.handleCommandEvent (/app.asar/src/command-registry.js:259:29)
at /app.asar/src/command-registry.js:3:59
at KeymapManager.module.exports.KeymapManager.dispatchCommandEvent (/app.asar/node_modules/atom-keymap/lib/keymap-manager.js:599:16)
at KeymapManager.module.exports.KeymapManager.handleKeyboardEvent (/app.asar/node_modules/atom-keymap/lib/keymap-manager.js:390:22)
at WindowEventHandler.module.exports.WindowEventHandler.handleDocumentKeyEvent (/app.asar/src/window-event-handler.js:106:36)
at /app.asar/src/window-event-handler.js:3:59)
```

### Commands

```
-2:09.2.0 command-palette:toggle (input.hidden-input)
3x -2:03.8.0 core:move-down (input.hidden-input)
-2:03.1.0 core:move-up (input.hidden-input)
-1:53.5.0 core:confirm (input.hidden-input)
-1:53.5.0 tablr:insert-column-after (input.hidden-input)
-1:48.7.0 core:undo (input.hidden-input)
2x -1:47 core:move-right (input.hidden-input)
-1:34.2.0 core:cancel (input.hidden-input)
-1:33.9.0 core:move-up (input.hidden-input)
-1:33.5.0 core:move-down (input.hidden-input)
-1:33.1.0 core:move-right (input.hidden-input)
-1:32.8.0 core:move-up (input.hidden-input)
-1:27.7.0 pane:show-next-item (input.hidden-input)
4x -1:25.8.0 tablr:insert-column-after (input.hidden-input)
4x -0:58.6.0 core:backspace (input.hidden-input)
-0:50.9.0 core:confirm (input.hidden-input)
```

### Non-Core Packages

```
atom-beautify 0.29.17
autocomplete-python 1.8.57
git-plus 7.3.3
language-matlab 0.2.1
language-r 0.4.1
language-restructuredtext 1.0.2
linter 1.11.23
linter-flake8 2.1.4
linter-markdown 3.1.0
linter-mixed-indent 1.1.0
markdown-writer 2.6.4
minimap 4.26.8
python-tools 0.6.9
Sublime-Style-Column-Selection 1.7.3
sync-settings 0.8.1
tablr 1.8.1
```