[MSHADE-248] shading fails with "error in opening zip file" if createSourcesJar=true and an invalid sources jar file is encountered

**[Ian Springer](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=ian.springer)** opened **[MSHADE-248](https://issues.apache.org/jira/browse/MSHADE-248?redirect=false)** and commented

```
Downloading: https://foo.repo.com/nexus/content/groups/foo/org/beanshell/bsh/2.0b4/bsh-2.0b4-sources.jar
[WARNING] Checksum validation failed, expected [Help 1]
```

bsh is a transitive dep of one of the jars I am shading. Since I can't control the fact that they have an invalid sources jar published, the shade plugin should be more forgiving and just log a warning and skip the bsh sources jar when building the shaded sources jar.

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**Affects:** 2.4.3

Reproduce the shade goal with createSourcesJar=true and an invalid transitive sources JAR, using the failure output as the starting point. Trace the source-JAR handling in the Maven Shade Plugin and verify that the invalid archive is skipped with a warning while the shaded sources JAR is still produced.

Written by the indexing model from the issue text.