hdf5_der

[svn-r20189] Addressed coverity defect 783.

H5SL_new_node() in H5SL.c was failing to free space allocated in its
first alloc if the second alloc failed.  Added a call to H5FL_FREE
to address this issue.

This is purely to keep coverity happy -- if this code is ever triggered,
we have much larger problems.

Note that this fix will trigger an unused return value complaint
from coverity next week.