src: reenable the assert() call
src: reenable the assert() call

`size_t` is always signed, so doing `unsigned size_t` was causing errors
with -Wall enabled.

cmpis/hiredis-node,erulabs/hiredis-node,badboy/hiredis-node-win,redis/hiredis-node,cmpis/hiredis-node,badboy/hiredis-node-win,BridgeAR/hiredis-node,iddar/hiredis-node,erulabs/hiredis-node,iddar/hiredis-node,BridgeAR/hiredis-node,redis/hiredis-node,kkoopa/hiredis-node,badboy/hiredis-node-win,iddar/hiredis-node,BridgeAR/hiredis-node,kkoopa/hiredis-node,cmpis/hiredis-node,kkoopa/hiredis-node,redis/hiredis-node,erulabs/hiredis-node