Issue with multibyte files

[ubaldot]

Consider the folllowing string:

**需要某种特定风格或主题**

By placing the cursor on the 6th character and by running echo synIDattr(synID(line("."), charcol("."), 1), "name"), then I get markdownBold.

Next, consider the following string:

需要**某种特定风格或主题**

By placing the cursor on the 6th character and by running echo synIDattr(synID(line("."), charcol("."), 1), "name"), then I don't get anything.

Nevertheless, if I consider an ASCII string, like the following:

unapar**olamolto**lunga

By placing the cursor on col 12 and by running echo synIDattr(synID(line("."), charcol("."), 1), "name"), then I get markdownBold.