`changeEmphasis:` in text editors not working for forward selection before already analogously emphasized text

[LinqLover]

STR:

1. 'abc' asText
   	addAttribute: TextEmphasis bold from: 3 to: 3;
   	edit

2. Forward-select ab (from left to right)
3. Press Cmd+7 (for bold)

Expected: ab is bold

Actual: Nothing changes

This is due to TextEditor>>#changeEmphasis: determining the previous attributes from the character at the point index, being c in this case. Probably it should collect the attributes within the entire ranges instead and then toggle their global appearance (some -> all -> none -> all -> ...).