Simple fixes to reduce memory consumption.

[VadimZhestikov]

As primary test was used following test-fill-array script, and bench4 script:

function init(size) {
    var o = {};
    for (var i=0; i<size; i++) {
        o[`some_property${i}`] = i;
    }
}

function handler() {
    var size = ("undefined" == typeof scriptArgs) ? Number(process.argv[2]):
       Number(scriptArgs[1]);

    console.log('init size='+size);

    init(size);
}

handler();

As additional test was used bench4 testsuite.

############### test-fill-array 1000000

qjs
init size=1000000
RSS:91452kb

njs (this patch)
init size=1000000
RSS:239024kb

njs (before this patch)
init size=1000000
RSS:607508kb

njs v0.8.9 (before "atomic patch")
init size=1000000
RSS:499816kb

############### bench4

qjs
Richards: 898
Crypto: 1060
RayTrace: 1003
NavierStokes: 1913
----
Score (version 9): 1162
RSS:6420kb

njs (this patch)
Richards: 634
Crypto: 1014
RayTrace: 501
NavierStokes: 1553
----
Score (version 9): 841
RSS:2697088kb

njs (before this patch)
Richards: 564
Crypto: 952
RayTrace: 494
NavierStokes: 1440
----
Score (version 9): 786
RSS:2830720kb

njs v0.8.9 (before "atomic patch")
Richards: 361
Crypto: 853
RayTrace: 363
NavierStokes: 1309
----
Score (version 9): 618
RSS:3026688kb

Fixes for memory consumption in flathsh will be added soon.