Avoided to convert empty PVD components copyright_file_id, abstract_file_id, or

bibliographic_file_id to " " and then "_" during multi-session loading and
writing. New util function iso_util_strcopy_untail().

libisofs/util.c

@@ -1392,13 +1392,36 @@ char *strcopy(const char *buf, size_t len)
     strncpy(str, buf, len);
     str[len] = '\0';
     
-    /* remove trailing spaces */
+    /* remove trailing spaces
+       (This leaves the space at str[0] existing. Bug or feature ?)
+    */
     for (len = len-1; str[len] == ' ' && len > 0; --len)
         str[len] = '\0'; 
     
     return str;
 }
 
+char *iso_util_strcopy_untail(const char *buf, size_t len)
+{
+    char *str;
+    
+    str = malloc((len + 1) * sizeof(char));
+    if (str == NULL) {
+        return NULL;
+    }
+    strncpy(str, buf, len);
+    str[len] = 0;
+    
+    /* remove trailing spaces */
+    for (len = len-1; len >= 0; --len) {
+        if (str[len] != ' ')
+    break;
+        str[len] = 0; 
+    }
+    
+    return str;
+}
+
 /**
  * Copy up to \p max characters from \p src to \p dest. If \p src has less than
  * \p max characters, we pad dest with " " characters.