Fix parsing of empty colon-separated fields, reported by Siarhei Siniak.

input.c

@@ -1862,7 +1862,8 @@ input_csi_dispatch_sgr_colon(struct input_ctx *ictx, u_int i)
 				free(copy);
 				return;
 			}
-		}
+		} else
+			n++;
 		log_debug("%s: %u = %d", __func__, n - 1, p[n - 1]);
 	}
 	free(copy);