undo: fix off-by-one when prepending to inline string
This fixes the conditional in istring_prepend() to match other uses, notably to match istring_append().
Fixes #6684 (closed)
This is a good candidate for cherry-picking to stable branches too.
This fixes the conditional in istring_prepend() to match other uses, notably to match istring_append().
Fixes #6684 (closed)
This is a good candidate for cherry-picking to stable branches too.