fix(ui): prevent crash when opening line visualization options
fix(ui): prevent crash when opening line visualization options

For whatever reason, we now have xy views stored with an empty array in
the `colors` field. Attempting to open the visualization options for
such a view results in a crash.

This commit updates the `ColorSchemeDropdown` to access the `colors`
field more defensively.

Closes #14950

nooproblem/influxdb,nooproblem/influxdb,li-ang/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,influxdata/influxdb,li-ang/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,nooproblem/influxdb,influxdb/influxdb,nooproblem/influxdb,influxdata/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb