Don't show the expand icon if a header isn't expandable.
If multiple sections of collapsed context exist within a single function, the

headers listed in the collapsed sections will be the same function name, but

only the first one is expandable. Unfortunately, the "+" icon was still shown,

despite it not having an <a> tag around it.

Loaded a diff where I noticed this issue. Saw that the function name was still

shown, but the expand icon was gone.