[m-rev.] diff: document exception conditions for array.init/3 and array.generate/2

[Julien Fischer]

Document exception conditions for array.init/3 and array.generate/2.

library/array.m:
     Document that the above will throw an exception if their first
     argument is < 0.

Julien.

diff --git a/library/array.m b/library/array.m
index f0a8c4d..6a89a0e 100644
--- a/library/array.m
+++ b/library/array.m
@@ -91,7 +91,8 @@
  :- func make_empty_array = (array(T)::array_uo) is det.

      % init(Size, Init, Array) creates an array with bounds from 0
-    % to Size-1, with each element initialized to Init.
+    % to Size-1, with each element initialized to Init.  Throws an
+    % exception if Size < 0.
      %
  :- pred init(int, T, array(T)).
  :- mode init(in, in, array_uo) is det.
@@ -111,7 +112,7 @@
      % Create an array with bounds from 0 to Size - 1 using the function
      % Generate to set the initial value of each element of the array.
      % The initial value of the element at index K will be the result of
-    % calling the function Generate(K).
+    % calling the function Generate(K). Throws an exception if Size < 0.
      %
  :- func generate(int::in, (func(int) = T)::in) = (array(T)::array_uo)
      is det.