InstallLib error for new shared libraries

When using the Library.nsh InstallLib macro, a new
shared library causes the error flag to be set.

I traced the problem to a bug within Library.nsh. The
ReadRegDword instruction (line 223) for incrementing
the shared count will fail when a library is brand new (no
registry entry yet). There is a subsequent ClearErrors
instruction in the code. But it doesn't get executed for
new libraries.