translate: fix stutter-invariant flag on leading Xs

Issue discovered by Mikuláš Klokočka and reported by František
Blahoudek.

* spot/twaalgos/translate.cc: Reset the stutter-invariant flag
when adding extra transitions for leading Xs.
* tests/core/stutter-tgba.test: New test case.
* NEWS: Mention the bug.
17 jobs for next in 451 minutes and 42 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed alpine-gcc #25106

00:21:29

passed arch-clang #25107

00:37:57

passed arch-gcc-glibcxxdebug #25125

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passed debian-gcc-snapshot #25105

00:58:46

passed debian-stable-gcc #25103

00:29:54

passed debian-unstable-gcc-coverage #25104

00:33:39

88.8%
passed debpkg-stable #25111

03:20:33

passed debpkg-unstable #25169

03:35:15

passed mingw-shared #25109

00:08:50

passed mingw-static #25110

00:07:39

passed rpm-pkg #25113

00:48:29

failed arch-gcc-glibcxxdebug #25108

00:37:37

failed debpkg-unstable #25168

02:18:48

failed debpkg-unstable #25124

01:59:17

failed debpkg-unstable #25112

02:21:33

 
  Publish
passed publish-rpm #25114
dput

00:00:18

passed publish-unstable #25115
dput

00:01:56