fixed GC bug with big files and unwanted buffer overwrite bug.
fixed GC bug with big files and unwanted buffer overwrite bug.

MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,bluerover/6lbr,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki