soup-message-io: fix crash when doing unpause+cancel
soup-message-io: fix crash when doing unpause+cancel

soup_message_io_stop() was unreffing unpause_source (if it was set),
but it didn't actually own a ref on it, so this would crash.
Fortunately this would only happen if you unpaused a message and then
immediately cancelled it, which isn't very common. Fixes a sporadic
chunk-test crash though.

jwendell/libsoup,Distrotech/libsoup,fanc999/libsoup,fanc999/libsoup,Distrotech/libsoup,Distrotech/libsoup,jwendell/libsoup,jwendell/libsoup,jwendell/libsoup,fanc999/libsoup,Distrotech/libsoup,fanc999/libsoup,Distrotech/libsoup,fanc999/libsoup,jwendell/libsoup