Added guard against missing call and moved alength assignment in fetchInit.

Added guard against missing call and moved alength assignment in fetchInit.

The returned value of rx_NewCall is important of course and must be taken
into account before trying to start RPCs. Do assign the length output
variable ASAP.
Also fixes an overlong line and the type of the pos local var to unsigned.

More style fixes:
* Moved length64 to use proper scope, initialized code.
* Generally make more tidy

Reviewed-on: http://gerrit.openafs.org/128
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>