[mod_unimrcp] Fix to ignore connections with null sockets

[ipsoft-rmcevoy]

Changes to resolve #196 according to the unimrcp commit for the same issue

While #1071 also aims to cover this fix, it is a significantly sized pull request which has been open for many months, and changes a lot more files. The base fix, which we have included here, is much smaller and simpler of a change, and we hope it can be accommodated in the next releases

[andywolk]

Please rebase your branch against upstream master

[signalwire-ci[bot]]

Unit-tests failed: https://public-artifacts.signalwire.cloud/drone/signalwire/freeswitch/291/artifacts.html

[seven1240]

code moved to https://github.com/freeswitch/mod_unimrcp , please open a new in the new repo.