BUG #14835: Rescale custom range as needed when using log.

When log scaling is enabled on the color map, if user specifies a custom
range that is invalid, use the same range scaling logic as when toggling
to use log-scale as described in the bug report for BUG #14835.

Change-Id: Idbfe340d2635f5e2a88e30e88eed62edbdd999be
Merge topic '14835_fix_log_scale_for_coloring' into next

21b340fb BUG #14835: Rescale custom range as needed when using log.