soup-session.c: do not emit content-sniffed if it isn't cached
soup-session.c: do not emit content-sniffed if it isn't cached

The SoupCache does not get any information from sniffed content types as it
works at a lower level. That's why sometimes we might not have any
Content-Type information for a cached resource (if the server does not
specify it).

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