allocator is out of memory

[yangfar]

Describe the issue
When i test the test_tinyexr with afl++, some crashes arose in tinyexr.h:5779.

To Reproduce
Steps to reproduce the behavior:
$ git clone https://github.com/syoyo/tinyexr.git
$ cd tinyext
$ export CFLAGS="-fsanitize=address"
$ export CXXFLAGS="-fsanitize=address"
$ export CC=afl-clang-fast
$ export CXX=afl-clang-fast++
$ export AFL_USE_ASAN=1
$ mkdir build
$ cd build
$ make -j8
Compile TinyEXR with Address Sanitizer

run
./test_tinyexr ./poc

Environment
OS: Ubuntu 20.04.2 LTS
gcc: 9.4.0

Error

`==3255101==ERROR: AddressSanitizer: allocator is out of memory trying to allocate 0x7989cbf5f0 bytes
#0 0x495e8d in malloc (/home/yzy/fuzzsoftware/tinyexr-release/test_tinyexr+0x495e8d)
#1 0x528c93 in tinyexr::AllocateImage(int, TEXRChannelInfo const*, int const*, int, int, bool*) /home/yzy/fuzzsoftware/tinyexr-release/./tinyexr.h

==3255101==HINT: if you don't care about these errors you may set allocator_may_return_null=1
SUMMARY: AddressSanitizer: out-of-memory (/home/yzy/fuzzsoftware/tinyexr-release/test_tinyexr+0x495e8d) in malloc
==3255101==ABORTING`

Poc

Poc.zip

[syoyo]

#198