Arc colors setting in Gauge chart report is not robust

[nielsdejong]

In the Gauge chart report, the "comma-separated arc colors" only work with (comma+space)-separated colors:
#fa7970, #faa356, #f4d47c, #7ce38b = OK
#fa7970,#faa356,#f4d47c,#7ce38b = NOK => 4 black arcs