Lock native float16 dtype only if available.
https://github.com/h5py/h5py/issues/2419
https://github.com/h5py/h5py/pull/2422
--- h5py/api_types_hdf5.pxd
+++ h5py/api_types_hdf5.pxd
@@ -385,6 +385,8 @@ cdef extern from "hdf5.h":
 
 # === H5I - Identifier and reflection interface ===============================
 
+  int H5I_INVALID_HID
+
   IF HDF5_VERSION < VOL_MIN_HDF5_VERSION:
     ctypedef enum H5I_type_t:
       H5I_UNINIT       = -2,  # uninitialized Group
--- h5py/h5i.pyx
+++ h5py/h5i.pyx
@@ -18,6 +18,7 @@ from ._objects import phil, with_phil
 
 # === Public constants and data structures ====================================
 
+INVALID_HID = H5I_INVALID_HID
 BADID       = H5I_BADID
 FILE        = H5I_FILE
 GROUP       = H5I_GROUP
--- h5py/h5t.pyx
+++ h5py/h5t.pyx
@@ -232,7 +232,10 @@ LDOUBLE_BE.set_order(H5T_ORDER_BE)
 LDOUBLE_BE.lock()
 
 IF HDF5_VERSION > (1, 14, 3):
-    NATIVE_FLOAT16 = lockid(H5T_NATIVE_FLOAT16)
+    if H5T_NATIVE_FLOAT16 != H5I_INVALID_HID:
+        NATIVE_FLOAT16 = lockid(H5T_NATIVE_FLOAT16)
+    else:
+        NATIVE_FLOAT16 = H5I_INVALID_HID
 
 # Unix time types
 UNIX_D32LE = lockid(H5T_UNIX_D32LE)