Update command/backtrace.sh

Co-authored-by: Joachim Ansorg <github@ja-dev.eu>

Author: rocky

command/backtrace.sh

@@ -170,7 +170,7 @@ function _Dbg_do_backtrace {
 	    lineno=${BASH_LINENO[$adjusted_pos-1]}
 	fi
 	filename="$(_Dbg_resolve_expand_filename "${BASH_SOURCE[$adjusted_pos]}")"
-	filename=$(_Dbg_adjust_filename "$filename")
+	filename="$(_Dbg_adjust_filename "$filename")"
 	_Dbg_msg "($_Dbg_parm_str) called from file \`$filename'" "at line $lineno"
 	if (( show_source )) ; then
 	    _Dbg_get_source_line $lineno "${BASH_SOURCE[$adjusted_pos]}"