MuonCondAlg: Protect against unknown MDT station.

In MuonAlignmentCondAlg, skip lines from the JSON blob that don't
translate to a valid identifier.

In the test_bulkProcessing_splashes art test, we were getting EIS stations
from the JSON blob, while they didn't exist in the detector description.
The code was trying to convert the resulting (invalid) identifier
to a string for a diagnostic.  Recent Identifier changes resulted
in this crashing with an out-of-bounds exception.  Now handle
this by printing a warning.

Note that this test was already printing warnings like::

```
  MGM::MuonDetectorManager                               0     0 WARNING BLinePar with AmdbId Muon B-Line deformation AMDB id (name,eta,phi,job)=(EIL,-3,2,0),  tube bow in plane bz=0.032, tube bow out of plane bp=0, bn=0, cross plate sage out of plane sp=0, sn=0, twist tw=0, parallelogram pg=0, trapezoid tz=0, global expansion eg=0.085, local expansion ep=0.002, en=-0.001 *** No MuonStation found 
 PLEASE CHECK FOR possible MISMATCHES between alignment constants from COOL and Geometry Layout in use
```

so there may still be a problem with the conditions tag.
Regardless, though, we shouldn't die with an out-of-bounds exception.