ARXML: two minor fixes
ARXML: two minor fixes

- Do not catch arbitrary exceptions if parsing a number string goes
  wrong, just `ValueError`
- Do not puke if the initial value of a signal cannot be parsed, only burp
  (i.e., produce a warning)

Signed-off-by: Andreas Lauser <429495c8e182c230dc2e2e45b7683abab22a535c@mbition.io>
Signed-off-by: Oliver Kopp <145f9cd3bd4b8f6f87f6a0c88db241a6cbaa88bd@mbition.io>

cantools/cantools,eerimoq/cantools