Tags can be edited to have empty icons, making them invisible in the view

[galenbwill]

Version and Platform (required):

• Binary Ninja Version: 5.0.7208-dev Ultimate (9967e4cb)

Bug Description:
After creating a tag type, double-clicking the icon in the Tag Types tab of the tag list sidebar, the icon can be set to arbitrary text, including no text. Then when a tag of this type is created in a view, it is not visible in the gutter, and hovering does not show that there is a tag present.

Selecting Show Tags at Location... from the context menu does show the tag, and the tag appears in the appropriate sub-list in the Tags tab of the tag list sidebar.

Steps To Reproduce:
Please provide all steps required to reproduce the behavior:

1. Tag list sidebar
2. Click on Tag Types tab
3. Select Create Tag Type from the right-click menu
4. Double click on the icon of the newly created tag
5. Delete the text present and hit enter
6. Select any location in a view (linear or graph), right click, Add Tag, and select the new tag type
7. Observe that the newly created tag does not appear in the view, nor when hovering over the gutter, but does exist in the Tags list and when showing tags at the location.

Expected Behavior:
Either:

1. Tags with empty icon text should still (somehow?) be represented in the view gutter, or
2. It should be an error to set the text of an icon to the empty string.