common : fix improper trimming in XML parser on complete message (#19805)

Co-authored-by: Jules LEIDELINGER <11395311+julio75012@users.noreply.github.com>

common/chat-parser-xml-toolcall.cpp

@@ -803,7 +803,7 @@ inline void parse_msg_with_xml_tool_calls(common_chat_msg_parser & builder, cons
         }
 
         // remove potential partial suffix
-        if (builder.pos() == builder.input().size()) {
+        if (builder.pos() == builder.input().size() && builder.is_partial()) {
             if (unclosed_reasoning_content.empty()) {
                 rstrip(content);
                 trim_potential_partial_word(content);