dump_to_dict not working for empty dump subdirs

Example:

In /var/lib/phosphor-debug-collector/dumps, there are the following
subdirectories.  However, 11 is empty.

11  12  13  14  15  16

Change-Id: Ifca568de68ad62e5492b79aae2f01edd7ee431da
Signed-off-by: Michael Walsh <micwalsh@us.ibm.com>
diff --git a/lib/dump_utils.py b/lib/dump_utils.py
index 536b73e..0c4a880 100755
--- a/lib/dump_utils.py
+++ b/lib/dump_utils.py
@@ -49,8 +49,9 @@
 
     quiet = int(gp.get_var_value(quiet, 1))
     cmd_buf = "dump_dir_path=" + var.DUMP_DIR_PATH + " ; " \
-              + "for dump_id in $(ls ${dump_dir_path} | sort -n) ; " \
-              + "do echo -n $dump_id: ; ls ${dump_dir_path}${dump_id}/* ; done"
+              + "for dump_id in $(ls ${dump_dir_path} | sort -n) ; do " \
+              + "file_path=$(ls ${dump_dir_path}${dump_id}/* 2>/dev/null)" \
+              + " || continue ; echo ${dump_id}:${file_path} ; done"
     output, stderr, rc = bsu.bmc_execute_command(cmd_buf, quiet=quiet)
 
     return vf.key_value_outbuf_to_dict(output)