storeChunk with zero extent

**Describe the bug**
When calling `storeChunk` with a zero extent, bad things happen.

Have to check again, but either some backends crashed, hung or were made `empty()`.

**To Reproduce**
Re: https://github.com/ECP-WarpX/WarpX/pull/1898#discussion_r745008290

Python:
```python
import openpmd_api

# ...
```
or C++
```C++
#include

// ...
```

or command line script, example:
```bash
# in directory $HOME/src/openPMD-api
mkdir build && cd build

cmake ..
# fails with:
# bash: cmake: command not found
```

**Expected behavior**
A clear and concise description of what you expected to happen.

**Software Environment**
- version of openPMD-api: 0.14.3
- installed openPMD-api via: any
- operating system: Linux
- machine: Ubuntu
- name and version of Python implementation: N/A
- version of HDF5: [e.g. 1.12.0]
- version of ADIOS1: [e.g. 1.13.1]
- version of ADIOS2: [e.g. 2.7.1]
- name and version of MPI: [e.g. OpenMPI 4.1.1]

**Additional context**
Re: https://github.com/ECP-WarpX/WarpX/pull/1898#discussion_r745008290