Fix: catch exception while handling incoming request

[codecov[bot]]

Codecov Report

Base: 92.47% // Head: 92.51% // Increases project coverage by +0.03% :tada:

Coverage data is based on head (d30787a) compared to base (943481d). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #28 +/- ## ============================================ + Coverage 92.47% 92.51% +0.03% - Complexity 1906 1907 +1 ============================================ Files 125 125 Lines 4241 4246 +5 Branches 608 608 ============================================ + Hits 3922 3928 +6 Misses 180 180 + Partials 139 138 -1 ``` | [Impacted Files](https://codecov.io/gh/open-coap/java-coap/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap) | Coverage Δ | | |---|---|---| | [...src/main/java/com/mbed/coap/server/CoapServer.java](https://codecov.io/gh/open-coap/java-coap/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap#diff-Y29hcC1jb3JlL3NyYy9tYWluL2phdmEvY29tL21iZWQvY29hcC9zZXJ2ZXIvQ29hcFNlcnZlci5qYXZh) | `100.00% <100.00%> (ø)` | | | [...c/main/java/com/mbed/coap/server/RescueFilter.java](https://codecov.io/gh/open-coap/java-coap/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap#diff-Y29hcC1jb3JlL3NyYy9tYWluL2phdmEvY29tL21iZWQvY29hcC9zZXJ2ZXIvUmVzY3VlRmlsdGVyLmphdmE=) | `100.00% <100.00%> (ø)` | | | [.../coap/transport/javassl/SocketClientTransport.java](https://codecov.io/gh/open-coap/java-coap/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap#diff-Y29hcC10Y3Avc3JjL21haW4vamF2YS9jb20vbWJlZC9jb2FwL3RyYW5zcG9ydC9qYXZhc3NsL1NvY2tldENsaWVudFRyYW5zcG9ydC5qYXZh) | `74.24% <0.00%> (+1.51%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-coap)

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