Lower the lower bound for introducing versions for electrum issue

Change in 2.6.3->2.6.4 for the damon was fixing one part of the damon
relative to the jsonprc. In 2.6 the RequestHandler was moved to the
damon part so mark at least 2.6 as well as problematic. This might be
not fully correst still but is inline with the upstream advisory
claiming only versions starting from 2.6 are affected.