py/repl: Enter four spaces when there are no matches.

Originally at adafruit#1859

Signed-off-by: scottbelden <scottabelden@gmail.com>

py/repl.c

@@ -228,6 +228,10 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
 
             // nothing found
             if (q_first == 0) {
+                if (s_len == 0) {
+                    *compl_str = "    ";
+                    return 4;
+                }
                 // If there're no better alternatives, and if it's first word
                 // in the line, try to complete "import".
                 if (s_start == org_str) {