Rejection of numeric groupnames aborts probably expensive calculations

[westram]

Reproduce:

• use a containing numeric groupnames (e.g. the that comes with SILVA_138.1_SSURef_NR99_12_06_20_opt.arb)
• mark some species that are in the
• call Tree/Remove species from tree/Remove marked.
  This will pop up the following message:

  11:32.39  Invalid group name '661256' (would be misinterpreted as plain inner node with a support value of 66% if re-imported from newick file)
  

  The marked species seem to be removed from .
• Now call Tree/Tree admin, then select << none >> and after that, again select the existing
  ⇒ all removed species re-appear!

Warning: If you encounter the above error message, you should fix these group names ASAP!

All operations modifying trees will be aborted, i.e. have no effect, as long as such groups exist.

Proposed fix:

If such a group exists, do not abort with an error under all conditions:

• attempts to save a newick shall refuse to do so (report error).
• saving a after ARB-Parsimony/quick-add shall save the with bad groups (just warn).
• …

---

related: #832
introduced by: [19282]

[westram]

Also reported by #862