hl: address bmribler review comments on PR HDFGroup#6371

- Replace "NUL termination" with "null termination" in comments
  (H5DS.c lines 2291, 2501; H5IM.c line 1029) to match codebase
  convention (H5T_STR_NULLTERM)
- Add clarifying comment in H5TBget_field_info else-branch explaining
  that name_len+1 <= HLTB_MAX_FIELD_LEN and that callers must provide
  buffers of at least HLTB_MAX_FIELD_LEN bytes (documented in H5TBpublic.h)

Author: brtnfld

hl/src/H5DS.c

@@ -2288,7 +2288,7 @@ H5DSis_scale(hid_t did)
             goto out;
         }
 
-        /* Allocate one extra byte and force NUL termination so strcmp never
+        /* Allocate one extra byte and force null termination so strcmp never
          * reads past the buffer even if some tool wrote the attribute without
          * honoring the H5T_STR_NULLTERM invariant. */
         buf = (char *)malloc((size_t)string_size * sizeof(char) + 1);
@@ -2498,7 +2498,7 @@ H5DS_is_reserved(hid_t did, bool *is_reserved)
     /* Allocate buffer large enough to hold string */
     if ((string_size = H5Tget_size(tid)) == 0)
         goto error;
-    /* Allocate one extra byte and force NUL termination so strcmp never
+    /* Allocate one extra byte and force null termination so strcmp never
      * reads past the buffer even if some tool wrote the attribute without
      * honoring the H5T_STR_NULLTERM invariant. */
     if (NULL == (buf = malloc(string_size * sizeof(char) + 1)))

hl/src/H5IM.c

@@ -1026,7 +1026,7 @@ H5IM__class_attr_equals(hid_t loc_id, const char *dset_name, const char *expecte
     if ((storage_size = H5Aget_storage_size(aid)) == 0)
         goto out;
 
-    /* Allocate one extra byte; force NUL termination in case the attribute
+    /* Allocate one extra byte; force null termination in case the attribute
      * was written without honoring H5T_STR_NULLTERM. */
     attr_data = (char *)malloc((size_t)storage_size * sizeof(char) + 1);
     if (attr_data == NULL)

hl/src/H5TB.c

@@ -3038,6 +3038,9 @@ H5TBget_field_info(hid_t loc_id, const char *dset_name, char *field_names[], siz
                 field_names[i][HLTB_MAX_FIELD_LEN - 1] = '\0';
             }
             else {
+                /* name_len < HLTB_MAX_FIELD_LEN, so name_len + 1 <= HLTB_MAX_FIELD_LEN.
+                 * Callers must provide buffers of at least HLTB_MAX_FIELD_LEN bytes each
+                 * (documented in H5TBpublic.h), so this copy is within bounds. */
                 memcpy(field_names[i], member_name, name_len + 1);
             }
             H5free_memory(member_name);