This was evidenced by an 'assert' failure, that the type was not an 'int'!
And also in the -xml-help output, thus effecting the tidy.1 manual page
for this new feature --vertical-space auto, which produces almost single
line html output.
This 'fix' began in the issue-228 branch - see Issue #231
This is when setting a String config value through say tidyOptSetValue
using say tidyOptSetValue(tdoc,id,"").
If the length of the new string is zero then do not allocate a 1 byte
buffer, set it to 0, for the option. Any previous buffer has already been
released.
This means API functions like tidyOptSaveSink will not return erroneous
null String values!
