Handle early eCAP transaction failures better.

Handle early eCAP transaction failures better.

Do not throw an exception if eCAP transaction had to deal with a virgin body
but was not consuming it at swangSong() time. This may happen if the eCAP
adapter throws an exception before the adapter requests the virgin body
transmission or after it stops the transmission. In other words, the
transaction wrapper consumes only if proxyingVb is on.

Merged from trunk r11118.