cmd_editor: fix cmd_buffer overflow and serial-ring skip on long input

Typing or pasting a line of 128 characters or more into the CLI hangs the
editor and overruns cmd_buffer[128]: the length check did not reserve room
for the terminating NUL written on Enter, and on a full buffer the character
was retried via continue without advancing the serial-ring read pointer at
the bottom of the loop, so input processing never caught up again.

Cap the line at CMD_BUF_SIZE-1 and, when full, drop the character but fall
through to consume the ring byte instead of spinning on it. The functional
change is three lines; the rest of the diff is re-indentation of the
insert-and-echo block (git diff -w shows the minimal form).

cmd_editor.c

@@ -40,8 +40,10 @@ void cmd_edit(void) __banked
 {
 	while (l != sbuf_ptr) {
 		if (sbuf[l] >= ' ' && sbuf[l] < 127) { // A printable character, copy to command line
-			if (cmd_line_len >= CMD_BUF_SIZE)
+			// Reserve one byte for the terminating NUL written on Enter. When the
-				continue;
+			// line is full, drop the character but still fall through to advance the
+			// serial-ring read pointer below; a 'continue' here would spin forever.
+			if (cmd_line_len < CMD_BUF_SIZE - 1) {
 				write_char(sbuf[l]);
 				// Shift buffer to right
 				for (uint8_t i = cmd_line_len; i > cursor; i--)
@@ -55,6 +57,7 @@ void cmd_edit(void) __banked
 				// Move backwards
 				for (uint8_t i = cursor; i < cmd_line_len; i++)
 					write_char('\010'); // BS works like cursor-left
+			}
 		} else if (sbuf[l] == '\033') { // ESC-Sequence
 			// Wait until we have at least 3 characters including the ESC character in the serial buffer
 			if (((sbuf_ptr + SBUF_SIZE - l) & SBUF_MASK) < 3)