[m-rev.] diff: fix an abort in read_binary_file_as_bitmap

[Julien Fischer]

Fix an abort in read_binary_file_as_bitmap.

Reading a bitmap from a binary file stream where the stream is already at EOF
causes an abort rather than returning an empty bitmap in the case where the
file is a regular file.  (The case where the stream is not a regular file is
already handled correctly.)

library/io.m:
     Fix the above problem.

tests/hard_coded/read_bitmap_size.{m,exp}:
     Extend this test case to check for the above.

Julien.

diff --git a/library/io.m b/library/io.m
index a4469b2..995ddd7 100644
--- a/library/io.m
+++ b/library/io.m
@@ -3605,19 +3605,23 @@ read_binary_file_as_bitmap(Stream, Result, !IO) :-
          RemainingSize = FileSize - CurrentOffset,
          some [!BM] (
              !:BM = bitmap.init(RemainingSize * bits_per_byte),
-            read_bitmap(Stream, 0, RemainingSize,
-                !BM, BytesRead, ReadResult, !IO),
-            (
-                ReadResult = ok,
-                ( if BytesRead = RemainingSize then
-                    Result = ok(!.BM)
-                else
-                    Result = error(io_error(
+            ( if RemainingSize = 0 then
+                Result = ok(!.BM)
+            else
+                read_bitmap(Stream, 0, RemainingSize, !BM, BytesRead,
+                    ReadResult, !IO),
+                (
+                    ReadResult = ok,
+                    ( if BytesRead = RemainingSize then
+                        Result = ok(!.BM)
+                    else
+                        Result = error(io_error(
                          "io.read_binary_file_as_bitmap: incorrect file size"))
+                    )
+                ;
+                    ReadResult = error(Msg),
+                    Result = error(Msg)
                  )
-            ;
-                ReadResult = error(Msg),
-                Result = error(Msg)
              )
          )
      else
diff --git a/tests/hard_coded/read_bitmap_size.exp b/tests/hard_coded/read_bitmap_size.exp
index 5be7515..95bb8c7 100644
--- a/tests/hard_coded/read_bitmap_size.exp
+++ b/tests/hard_coded/read_bitmap_size.exp
@@ -3,3 +3,4 @@ SKIP 1: 00000010.00000100.00001000.00010000.00100000.01000000.10000000.11111111
  SKIP 2: 00000100.00001000.00010000.00100000.01000000.10000000.11111111
  SKIP 4: 00010000.00100000.01000000.10000000.11111111
  SKIP 8: 11111111
+SKIP 9: 
diff --git a/tests/hard_coded/read_bitmap_size.m b/tests/hard_coded/read_bitmap_size.m
index 3c63bce..05791be 100644
--- a/tests/hard_coded/read_bitmap_size.m
+++ b/tests/hard_coded/read_bitmap_size.m
@@ -40,7 +40,8 @@ main(!IO) :-
          do_test(1, !IO),
          do_test(2, !IO),
          do_test(4, !IO),
-        do_test(8, !IO)
+        do_test(8, !IO),
+        do_test(9, !IO)
      ;
          OpenResult = error(IOError),
          io.error_message(IOError, Msg),