Do not write after the end of the array and overwrite the stack when

colon-separated SGR sequences contain empty arguments. Reported by Sergey
Nizovtsev.

input.c

@@ -1976,8 +1976,13 @@ input_csi_dispatch_sgr_colon(struct input_ctx *ictx, u_int i)
 				free(copy);
 				return;
 			}
-		} else
+		} else {
 			n++;
+			if (n == nitems(p)) {
+				free(copy);
+				return;
+			}
+		}
 		log_debug("%s: %u = %d", __func__, n - 1, p[n - 1]);
 	}
 	free(copy);