'/v2/indigo/render' endpoint throws exception

**Steps to reproduce:**
1. Execute 'render' method with the following arguments:
struct:
[struct.txt](https://github.com/epam/Indigo/files/6122296/struct.txt)

options:
{
"smart-layout": true,
"ignore-stereochemistry-errors": true,
"mass-skip-error-on-pseudoatoms": false,
"gross-formula-add-rsites": true,
"outputFormat": "svg"
}

**Expected result:**
Base64 string is generated without any exceptions

**Actual result:**
500 HTTP code is gotten with the following description:
{
"error": "'NoneType' object has no attribute 'loadMolecule'"
}