python.pkgs.pythonNamespacesHook: check parent directory exists before removing child

pkgs/development/interpreters/python/hooks/python-namespaces-hook.sh

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             fi
 
             # remove ${pname}-${version}-${python-interpeter}-nspkg.pth
-            if [ -z ${dontRemovePth-} ]; then
+            #
+            # Still need to check that parent directory exists in the
+            # event of a "meta-package" package, which will just install
+            # other packages, but not produce anything in site-packages
+            # besides meta information
+            if [ -d "${constructedPath}/../" -a -z ${dontRemovePth-} ]; then
                 # .pth files are located in the parent directory of a module
                 @findutils@/bin/find ${constructedPath}/../ -name '*-nspkg.pth' -exec rm -v "{}" +
             fi