proto-stream.el (open-protocol-stream): Protect against the low-level transport funct...

proto-stream.el (open-protocol-stream): Protect against the low-level transport functions returning nil.
gnus-sum.el (gnus-summary-next-article): Remove hack to reselect group window, because it does the wrong thing when a separate frame displays the group buffer.
gnus-int.el (gnus-request-accept-article): Don't try to update marks and stuff if the backend didn't return the article number.  This fixes an Exchange-related nnimap bug.
mm-decode.el (mm-preferred-alternative-precedence): Discourage showing empty parts.
nnimap.el (nnimap-convert-partial-article): Protect against zero-length body parts.