[MNG-7436] Do not fail if there is one bad dependency

**[Christoph Läubrich](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=laeubi)** opened **[MNG-7436](https://issues.apache.org/jira/browse/MNG-7436?redirect=false)** and commented

We currently have a [bug-report at tycho](https://github.com/eclipse/tycho/issues/781) that complains about missing dependency resolution.
It seems that a dependency with system scope but missing path triggers this (something that should be fixed of course), but I think maven should be a bit more forgiven here:

Instead of failing completely, it should simply skip the "bad" dependency. If that's not feasible , in any case it should clearly indicate the causing item in the pom.

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No further details from [MNG-7436](https://issues.apache.org/jira/browse/MNG-7436?redirect=false)

Start by reproducing dependency resolution with a system-scoped dependency whose path is missing, using the POM scenario described in the issue. Trace the Maven dependency-resolution failure and determine whether the expected result is to skip the bad dependency or report the causing POM item clearly; done means the chosen behavior is covered by a regression test.

Written by the indexing model from the issue text.