cairo: Make sure we always push a transparency group in setSoftMaskFromImageMask()

Because that's what unsetSoftMaskFromImageMask() assumes.

https://bugs.freedesktop.org/show_bug.cgi?id=81624
annots: Fix a crash when adding annot without contents

Having no content in an annotation results in a crash when generating
its appearance, since the contents pointer is dereferenced.
For consistency, the same has been done in Annot::initialize.
glib: Return NULL in poppler_annot_get_contents also for empty strings
glib: Fix a memory leak when getting text layout and attributes
Don't check for inlineImg twice

Bug #82059
Improve non-latin characters in inline notes

Preview commit had by mistake changes in these two files that belong here

Bug #65956
Merge remote-tracking branch 'origin/poppler-0.26'