* lisp/erc/erc.el (erc--get-inserted-msg-bounds): Account for
`previous-single-property-change' returning a position adjacent to
that with an actual changed value. The prior attempt at addressing
this was insufficient.
* test/lisp/erc/erc-tests.el (erc--get-inserted-msg-bounds): New test.
; * test/lisp/erc/resources/base/local-modules/second.eld: Timeout.
; * test/lisp/erc/resources/base/local-modules/third.eld: Timeout.