small fixes, make default a noop

src/vm.c

@@ -269,16 +269,15 @@ bool step_vm(VM *vm) {
           vm->stack[++vm->sp].i = 0; /* error or no ioctl support */
         }
       }
-      break;
+      return true;
     }
 
     case SYSCALL_EXIT: {
       return false;
-      break;
     }
 
     default: {
-      regs[0].i = -1;
+      /* NOOP */
       return true;
     }
     }