fixes two bugs in the Memory module (#1272)

The first bug was breaking the raw loader at least. It bug was
introduced in #1178 during the `Memory.view` optimization. A check was
missed that allowed for creation of invalid views. The invalid views
later were caught with an assertion check, (easily reproduced with
`bap /bin/ls --loader=raw`), e.g.,

```
("Assert_failure bap_memory.ml:72:2"
  "Raised at file \"bap_memory.ml\", line 72, characters 2-31\
 \nCalled from file \"bap_memory.ml\", line 196, characters 2-18\
 \nCalled from file \"bap_memory.ml\", line 410, characters 26-52\
 \nCalled from file \"bap_trie.ml\", line 46, characters 34-53\
 \nCalled from file \"bap_trie.ml\", line 62, characters 4-130\
 \nCalled from file \"bap_byteweight.ml\", line 78, characters 12-39\
 \nCalled from file \"bap_byteweight.ml\", line 129, characters 12-39\
 \nCalled from file \"byteweight_main.ml\", line 50, characters 44-56\
 \nCalled from file \"src/sequence.ml\", line 123, characters 29-36\
 \nCalled from file \"byteweight_main.ml\" (inlined), line 49, characters 4-116\
 \nCalled from file \"byteweight_main.ml\", line 48, characters 4-146\
...
```

The second bug was probably all the time in the library and concerns
`Memory.find_map` and `Memory.find_if`, which are talking an optional
`word_size` parameter that was ignored and functions were always
iterating over bytes.

lib/bap_image/bap_memory.ml

@@ -213,7 +213,7 @@ module Input = struct
   let int256 = read `r256
 end
 
-let view_exn ?(word_size=`r8) ?from ?words  t =
+let view_exn ?(word_size=`r8) ?from ?words t =
   let amin = Option.value from ~default:(min_addr t) in
   let amax = match words with
     | None -> max_addr t
@@ -225,7 +225,7 @@ let view_exn ?(word_size=`r8) ?from ?words  t =
     if off >= t.off && off < t.off + t.size then match size with
       | 0 -> invalid_arg "empty view"
       | 1 -> make_byte t amin off
-      | n when n <= t.size ->
+      | n when n <= t.size && off + size <= t.off + t.size ->
         { t with size; data = t.data; addr = amin; off}
       | _ -> invalid_arg "out-of-bounds"
     else invalid_arg "out-of-bounds"
@@ -354,12 +354,12 @@ module Make_iterators( M : Monad.S) = struct
 
   let find_map ?word_size t ~f =
     with_return (fun s ->
-        iteri t ~f:(fun a w -> f a w >>= function
+        iteri ?word_size t ~f:(fun a w -> f a w >>= function
           | None -> return ()
           | some -> s.return (return some)) >>| fun () -> None)
 
   let find_if ?word_size t ~f =
-    find_map t ~f:(fun a w -> f a w >>| function
+    find_map ?word_size t ~f:(fun a w -> f a w >>| function
       | true  -> Some w
       | false -> None)
 end