[server] fix minor CLANG static analyzer bugs

These are simple logic fixes that would not have impacted run time to address
the following warnings generated by the CLANG static analyzer:

incoming_spa.c:433:17: warning: Value stored to 'attempted_decrypt' is never read
                attempted_decrypt = 1;
                ^                   ~
incoming_spa.c:647:13: warning: Value stored to 'acc' is never read
            acc = acc->next;
            ^     ~~~~~~~~~
[server] another minor CLANG static analyzer fix