fix a possible crash detected by coverity
(cherry picked from commit afff131bf7709a2f43fb46f517c34ada8767f78d)
Don't switch group if module activated via hotkey is already visible
(cherry picked from commit f93f9b4f2a434626f61e1e91d65c6ba0af22a290)
imageio_tiff: remove leftover assert
imageio_gm: clearly indicate when GraphicsMagick is being used