Tooltip was twice 'HTML escaped'

[albert-github]

The tooltip was already 'HTML escaped' except for some '<' and '>' characters but was again 'HTML escaped' resulting in e.g. that a single apostrophe (') was translated to ' and again to ' resulting in ' in the tooltip.
Only '<' and '>' are now 'HTML escaped again'

[doxygen]

Hi Albert, do you have an example of a twice escaped HTML tooltip, as I don't see it like that in the code?

I tried the following with SOURCE_BROWSER = YES:

/** @brief A class with > and < and &. */
class Test {};

[albert-github]

Hi Dimitri,

The description is so that only < and > have to be escaped again and not a character like &.

The example: pull_784_.zip

It is based on: https://stackoverflow.com/questions/43852075/doxygen-parsing-ampersands-for-ascii-chars
Just hover over the functions in the code.

[doxygen]

Looks like the problem is in TextDocVisitor::filter; this produces the unneeded escapes. So I've fixed this instead.

[albert-github]

Checked against the original problem as well (#378) and this looks still OK as well.