compilation fails with -DUSE_HDF5=AUTO

compilation with -DUSE_HDF5=AUTO (the default) leads to the following error when no HDF5 is found:

CMake Warning at cmake/FindHDF5.cmake:751 (message):
  HDF5 found for language C is parallel but previously found language is not
  parallel.
Call Stack (most recent call first):
  CMakeLists.txt:58 (find_package)


CMake Error at CMakeLists.txt:63 (message):
  Parallel HDF5 required, sequential HDF5 only found.  Please set
  -DBUILD_HDF5_PARALLEL=OFF to disable parallel HDF5

This is likely due to a leak of config variables from the unfound initial find.