BUG: MANTIS-1256: Disabled delete-all layers button when layer-stack is cleared.
BUG: MANTIS-1256: Disabled delete-all layers button when layer-stack is cleared.

orfeotoolbox/OTB,orfeotoolbox/OTB,orfeotoolbox/OTB,orfeotoolbox/OTB,orfeotoolbox/OTB,orfeotoolbox/OTB