fix: ignore dependencies without GVA for integration

[maxandersen]

if you use --class-path xyz.jar no GVA is present which currently makes integration calls fail.

This fixes it so NPE does not occur; but long term we should find a way to include classpath for integration calls.

[codecov]

Codecov Report

Merging #1350 (f506dd1) into main (e7391c1) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff            @@
##               main    #1350   +/-   ##
=========================================
  Coverage     56.52%   56.53%           
  Complexity     1165     1165           
=========================================
  Files           100      100           
  Lines          6172     6173    +1     
  Branches       1020     1021    +1     
=========================================
+ Hits           3489     3490    +1     
+ Misses         2203     2202    -1     
- Partials        480      481    +1     

Flag	Coverage Δ
Linux	55.27% <50.00%> (-0.08%)	⬇️
Windows	55.95% <50.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/main/java/dev/jbang/spi/IntegrationManager.java	18.00% <50.00%> (-0.13%)	⬇️
src/main/java/dev/jbang/util/JavaUtil.java	42.85% <0.00%> (+1.19%)	⬆️

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