patch 8.0.0993: sometimes an xterm sends an extra CTRL-X

Problem:    Sometimes an xterm sends an extra CTRL-X after the response for
            the background color.  Related to t_RS.
Solution:   Check for the CTRL-X after the terminating 0x7.
diff --git a/src/term.c b/src/term.c
index 6de4522..9e8bc3b 100644
--- a/src/term.c
+++ b/src/term.c
@@ -4626,6 +4626,10 @@
 			key_name[0] = (int)KS_EXTRA;
 			key_name[1] = (int)KE_IGNORE;
 			slen = i + 1 + (tp[i] == ESC);
+			if (tp[i] == 0x07 && i + 1 < len && tp[i + 1] == 0x18)
+			    /* Sometimes the 0x07 is followed by 0x18, unclear
+			     * when this happens. */
+			    ++slen;
 			break;
 		    }
 		if (i == len)