Clear screen: Fix edge case

With sequence \e[1J, if cursor is on second line, clear the first line.

st.c

@@ -1705,7 +1705,7 @@ csihandle(void)
 			}
 			break;
 		case 1: /* above */
-			if (term.c.y > 1)
+			if (term.c.y > 0)
 				tclearregion(0, 0, term.col-1, term.c.y-1);
 			tclearregion(0, term.c.y, term.c.x, term.c.y);
 			break;