msm: ipc: Access pointers after a successful check

Some pointers in msm_ipc_router_extract_msg function are accessed either
before a NULL pointer check or if one of the conditions in the check is
true.

Fix the code to dereference those pointers only after the pointer is not
NULL and the other associated conditions are true.

CRs-Fixed: 471110
Change-Id: Ic45fe118818caa6985e5e56403ab3cc467174cf6
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>