message: Fix: FindBlosc Env Hint
  The current check always returned true for the BLOSC_ROOT
  env var, even if it is unset.
diff: # as an environment variable.
  if(NOT BLOSC_FOUND)
  - if((NOT BLOSC_ROOT) AND (NOT (ENV{BLOSC_ROOT} STREQUAL "")))
  + if((NOT BLOSC_ROOT) AND (DEFINED ENV{BLOSC_ROOT}))
  set(BLOSC_ROOT "$ENV{BLOSC_ROOT}")
  endif()
  if(BLOSC_ROOT)
  