Fix so _VAL with no botschaftID is ignored
Fix so _VAL with no botschaftID is ignored

This fix targets .dbc files. Signals that are not used in any
messages have no id. Thus when trying to parse those signals
exceptions are thrown. This fix will ignore lines that start
with _VAL and has no id.

ebroecker/canmatrix,altendky/canmatrix,altendky/canmatrix,ebroecker/canmatrix