Fix segfault on VOL termination (#100)

* Initialize global type array ptr to NULL

src/rest_vol.c

@@ -99,7 +99,7 @@ typedef struct H5_rest_ad_info_t {
 } H5_rest_ad_info_t;
 
 /* Global array containing information about open objects */
-RV_type_info *RV_type_info_array_g[H5I_MAX_NUM_TYPES];
+RV_type_info *RV_type_info_array_g[H5I_MAX_NUM_TYPES] = {0};
 
 /* Host header string for specifying the host (Domain) for requests */
 const char *const host_string = "X-Hdf-domain: ";
@@ -629,11 +629,16 @@ H5_rest_term(void)
     } /* end if */
 
     /* Cleanup type info array */
-    for (size_t i = 0; i < H5I_MAX_NUM_TYPES; i++) {
-        rv_hash_table_free(RV_type_info_array_g[i]->table);
-        RV_free(RV_type_info_array_g[i]);
-        RV_type_info_array_g[i] = NULL;
+    if (RV_type_info_array_g) {
+        for (size_t i = 0; i < H5I_MAX_NUM_TYPES; i++) {
+            if (RV_type_info_array_g[i]) {
+                rv_hash_table_free(RV_type_info_array_g[i]->table);
+                RV_free(RV_type_info_array_g[i]);
+                RV_type_info_array_g[i] = NULL;
+            }
+        }
     }
+
     /*
      * "Forget" connector ID. This should normally be called by the library
      * when it is closing the id, so no need to close it here.