Prevent computations with tarval_bad.

This fixes opt/fehler206.c.

ir/opt/opt_osr.c

@@ -1156,6 +1156,12 @@ static ir_node *applyOneEdge(ir_node *iv, ir_node *rc, LFTR_edge *e, iv_env *env
 			panic("Unsupported opcode");
 		}
 
+		if (tv == tarval_bad || tv_init == tarval_bad) {
+			tarval_set_integer_overflow_mode(ovmode);
+			DB((dbg, LEVEL_4, " = OVERFLOW"));
+			return NULL;
+		}
+
 		if (pscc->code == iro_Add) {
 			tv_end = tarval_add(tv, tv_incr);
 		} else {
@@ -1165,7 +1171,7 @@ static ir_node *applyOneEdge(ir_node *iv, ir_node *rc, LFTR_edge *e, iv_env *env
 
 		tarval_set_integer_overflow_mode(ovmode);
 
-		if (tv == tarval_bad || tv_init == tarval_bad || tv_end == tarval_bad) {
+		if (tv_end == tarval_bad) {
 			DB((dbg, LEVEL_4, " = OVERFLOW"));
 			return NULL;
 		}