Server respond with 502 response status instead of 500 or other suitable for error case response.

**Steps to reproduce:**
1. Send POST request to https://lifescience.opensource.epam.com/v2/indigo/convert
with following payload
`{"struct":"\n\n \n \n \n \n \n \n \n \n \n \n \n \n\n","output_format":"chemical/x-mdl-molfile","options":{"smart-layout":true,"ignore-stereochemistry-errors":true,"mass-skip-error-on-pseudoatoms":false,"gross-formula-add-rsites":true}}`

**Actual result:**
502 Bad Gateway Response status is returned

**Expected result:**
500 Server error if conversion failed during execution or 400 Bad Request or whatever suitable