DirectAllocator: move if > 0 condition above @memcpy
DirectAllocator: move if > 0 condition above @memcpy

Minor improvement to 3c13aa17 as noted by daurnimator

raulgrell/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig