Dear all,

the attached trivial patch by Steve fixes a NULL pointer dereference
that occurs when an error shall be emitted for a global entity that
conflicts with a symbol appearing in a COMMON block, but the symbol's
location is not set.  This may happen e.g. in the testcase in the PR,
where the COMMON variables are imported from a module.

Regtested on x86_64-pc-linux-gnu with no failures.

I intend to commit as obvious within 24h unless there are comments.

Thanks,
Harald