lcms: avoid dereferencing null pointers

(cherry picked from commit d0f7e713bb4478f2da3a688abf89adfdc2a935ee)
color-selector-cmyk-lcms: avoid freeing uninitialized pointer

(cherry picked from commit c028580ae08ccf6408910ee6cf83d54308367f36)

Conflicts:
	modules/color-selector-cmyk.c
file-bmp: don't leak file pointer when erroring out

(cherry picked from commit 6467fbf65dd046ee71e210b664099234e03390b9)
gimpcolorwheel: comment out ineffectual code

(cherry picked from commit 1bb379c3f5ffbaada8942e71d1c333b9fcf5580a)
file-jpeg: fix operator precedence errors

(cf. commit a9376443d7a2530f4481be18ee96a0322dc01ae5)
app: don't ignore return value

...of gtk_widget_translate_coordinates()

(cherry picked from commit 391de600f1bd76aa21a3ec1ea4d349ef04cc160b)