Directly initialise initial arrays from time-dependent variables

[richfitz]

  gen <- odin::odin({
    initial(x1) <- norm_rand()
    r <- x1 * 2
    initial(x2[]) <- r + 1

    update(x1) <- x1
    update(x2[]) <- x2[i]

    dim(x2) <- 10
    config(base) <- "bug"
  })

throws

Error in 1L:after : result would be too long a vector
In addition: Warning message:
In max(which(names(time) == iv)) :
  no non-missing arguments to max; returning -Inf
> traceback()
5: append(time, tmp, at) at generate2.R#299
4: odin_generate2_initial(obj) at generate.R#34
3: odin_generate(dat, dest) at interface.R#141
2: odin_(xx, dest, build, verbose, compiler_warnings) at interface.R#130
1: odin::odin({
       initial(x1) <- norm_rand()
       r <- x1 * 2
       initial(x2[]) <- r + 1
       update(x1) <- x1
       update(x2[]) <- x2[i]
       dim(x2) <- 10
       config(base) <- "bug"
   }, verbose = TEST_VERBOSE)

[richfitz]

possible workaround for now is to edit odin_generate2_initial with

         if (any(!j)) {
+          stop("This is currently broken, though some models may work?")