added warning if zlib extension is not enabled

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | #1986, #2102, #2103 
| License       | MIT
| Doc PR        | -