input: don't take multiple keystrokes to be a single sequence

For some reason the keyboard code seems to assume that all integers
waiting in the keybuffer form a single sequence.  But this isn't the
case: when there is an escape (0x1b) among them, then that is where
a new sequence starts.  So, prevent the input code from considering
an escape after a non-escape as part of the current sequence.

This fixes https://savannah.gnu.org/bugs/?47839.

src/winio.c

@@ -370,7 +370,7 @@ int parse_kbinput(WINDOW *win)
 		case 1:
 		    /* Reset the escape counter. */
 		    escapes = 0;
-		    if (get_key_buffer_len() == 0) {
+		    if (get_key_buffer_len() == 0 || key_buffer[0] == 0x1b) {
 			/* One escape followed by a non-escape, and
 			 * there aren't any other keystrokes waiting:
 			 * meta key sequence mode.  Set meta_key to