print: remove assert in get_field_data().

The check in the caller suggests this function can fail. The
assert should not be necessary, then.

Bug: 16218
Change-Id: Ic2186f3c51751db61436719bbf5bce609d364d40
Reviewed-on: https://code.wireshark.org/review/35162
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

epan/print.c

@@ -1721,7 +1721,6 @@ get_field_data(GSList *src_list, field_info *fi)
             return tvb_get_ptr(src_tvb, fi->start, length);
         }
     }
-    g_assert_not_reached();
     return NULL;  /* not found */
 }