PDF Interpreter - Document and update previous work-around

The customer file has annotations with appearance streams which have
been compressed, but do not have a compression filter in the stream
dictionary. At least one of the streams has a ']' in the data, and
since we are interpreting the data directly this can correspond with a
matching mark on the stack, or throw an unmatched mark error.

Either way this can lead to stack corruption and other problems.

We did already execute the annotation in a stopped context, but if
that threw an error then, as part of the error recovery, we would run
a 'cleartomark'. If the stream had removed the mark we needed then that
would throw an error (which is what happens here).

Commit 4870aa85f14c900d47b5c1ba5eec48c64c384cad accidentally included
a patch to work around this by executing the error recovery inside a
stopped context so that we can recover from an error while recovering
from the previous error. This way madness lies......

This commit simply documents that previous accidental inclusion, and
adds a little more feedback for the user.

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