Update to nanopb 0.4.4

lib/nanopb/include/pb_common.h

@@ -32,6 +32,10 @@ bool pb_field_iter_next(pb_field_iter_t *iter);
  * Returns false if no such field exists. */
 bool pb_field_iter_find(pb_field_iter_t *iter, uint32_t tag);
 
+/* Find a field with type PB_LTYPE_EXTENSION, or return false if not found.
+ * There can be only one extension range field per message. */
+bool pb_field_iter_find_extension(pb_field_iter_t *iter);
+
 #ifdef PB_VALIDATE_UTF8
 /* Validate UTF-8 text string */
 bool pb_validate_utf8(const char *s);