Fix fusion prep from Dragen and Arriba inputs

[skanwal]

• Resolves https://github.com/umccr/RNAsum/issues/90
• Tried to introduce minimal updates to Master code base.
• Tested locally with following combination of fusions inputs
  • fusions called by both Dragen and Arriba
  • fusions called by only Dragen
  • fusions called by only Arriba
  • no fusions called by either Dragen or Arriba
• Next step will be to test on ICA with updated docker image

[victorskl]

Portal Release - Snowshoe: RNAsum Handle missing fusion calls