An issue was discovered in JerryScript 2.4.0. There is a SEVG in ecma_deref_bigint in ecma-helpers.c file.

###### JerryScript revision
2faafa4

###### Build platform
Ubuntu 18.04.5 LTS(Linux 4.15.0-119-generic x86_64)
###### Build steps
```
./tools/build.py --clean --debug --compile-flag=-fsanitize=address \
--compile-flag=-m32 --compile-flag=-fno-omit-frame-pointer \
--compile-flag=-fno-common --compile-flag=-g --strip=off \
--system-allocator=on --logging=on --linker-flag=-fuse-ld=gold \
--error-messages=on --profile=es2015-subset  --builddir=$PWD/build
```
###### Test case
```
var p = new Proxy(Function(), { get: function closure() { eval("o.p.y"); delete closure; return closure == arguments.callee && !(new String(undefined)); }});
Function.prototype.bind.call(p);
```
###### Output
```
ReferenceError: o is not defined
ASAN:DEADLYSIGNAL
=================================================================
==24756==ERROR: AddressSanitizer: SEGV on unknown address 0xbebebeb8 (pc 0x56782398 bp 0xff8c72d8 sp 0xff8c72b0 T0)
==24756==The signal is caused by a READ memory access.
    #0 0x56782397 in ecma_deref_bigint /root/jerryscript/jerry-core/ecma/base/ecma-helpers.c:1264
    #1 0x5677d2c5 in ecma_free_value /root/jerryscript/jerry-core/ecma/base/ecma-helpers-value.c:1147
    #2 0x567c10fc in ecma_gc_free_object /root/jerryscript/jerry-core/ecma/base/ecma-gc.c:1742
    #3 0x567c1e68 in ecma_gc_run /root/jerryscript/jerry-core/ecma/base/ecma-gc.c:1898
    #4 0x5678385a in ecma_finalize /root/jerryscript/jerry-core/ecma/base/ecma-init-finalize.c:83
    #5 0x567acb1d in jerry_cleanup /root/jerryscript/jerry-core/api/jerry.c:256
    #6 0x567a7a9c in main /root/jerryscript/jerry-main/main-unix.c:324
    #7 0xf774af20 in __libc_start_main (/lib32/libc.so.6+0x18f20)
    #8 0x566473d0  (/root/jerryscript/build/bin/jerry+0x1d3d0)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /root/jerryscript/jerry-core/ecma/base/ecma-helpers.c:1264 in ecma_deref_bigint
==24756==ABORTING
```

Credits: Found by chong from OWL337.
SEVG in  ecma_deref_bigint
This is a GitHub Issue
repo:jerryscript
owner:jerryscript-project
Title : SEVG in  ecma_deref_bigint
Issue date:

--- start body ---

###### JerryScript revision
2faafa4

###### Build platform
Ubuntu 18.04.5 LTS(Linux 4.15.0-119-generic x86_64)
###### Build steps
```
./tools/build.py --clean --debug --compile-flag=-fsanitize=address \
--compile-flag=-m32 --compile-flag=-fno-omit-frame-pointer \
--compile-flag=-fno-common --compile-flag=-g --strip=off \
--system-allocator=on --logging=on --linker-flag=-fuse-ld=gold \
--error-messages=on --profile=es2015-subset  --builddir=$PWD/build
```
###### Test case
```
var p = new Proxy(Function(), { get: function closure() { eval("o.p.y"); delete closure; return closure == arguments.callee && !(new String(undefined)); }});
Function.prototype.bind.call(p);
```
###### Output
```
ReferenceError: o is not defined
ASAN:DEADLYSIGNAL
=================================================================
==24756==ERROR: AddressSanitizer: SEGV on unknown address 0xbebebeb8 (pc 0x56782398 bp 0xff8c72d8 sp 0xff8c72b0 T0)
==24756==The signal is caused by a READ memory access.
    #0 0x56782397 in ecma_deref_bigint /root/jerryscript/jerry-core/ecma/base/ecma-helpers.c:1264
    #1 0x5677d2c5 in ecma_free_value /root/jerryscript/jerry-core/ecma/base/ecma-helpers-value.c:1147
    #2 0x567c10fc in ecma_gc_free_object /root/jerryscript/jerry-core/ecma/base/ecma-gc.c:1742
    #3 0x567c1e68 in ecma_gc_run /root/jerryscript/jerry-core/ecma/base/ecma-gc.c:1898
    #4 0x5678385a in ecma_finalize /root/jerryscript/jerry-core/ecma/base/ecma-init-finalize.c:83
    #5 0x567acb1d in jerry_cleanup /root/jerryscript/jerry-core/api/jerry.c:256
    #6 0x567a7a9c in main /root/jerryscript/jerry-main/main-unix.c:324
    #7 0xf774af20 in __libc_start_main (/lib32/libc.so.6+0x18f20)
    #8 0x566473d0  (/root/jerryscript/build/bin/jerry+0x1d3d0)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /root/jerryscript/jerry-core/ecma/base/ecma-helpers.c:1264 in ecma_deref_bigint
==24756==ABORTING
```

Credits: Found by chong from OWL337.
--- end body ---
