runtime(termdebug): using wrong type for PlaceSign()

Make sure to convert them to numbers.

fixes: #14994
closes: #15015

Signed-off-by: shane.xb.qian <shane.qian@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim b/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
index d6cf327..5bde69a 100644
--- a/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
+++ b/runtime/pack/dist/opt/termdebug/plugin/termdebug.vim
@@ -1949,7 +1949,7 @@
   for [id, entries] in items(breakpoints)
     for [subid, entry] in items(entries)
       if entry['fname'] == fname
-        PlaceSign(id, subid, entry)
+        PlaceSign(str2nr(id), str2nr(subid), entry)
       endif
     endfor
   endfor