combase: Fix reading from beyond the end of a HGLOBAL stream.

dlls/combase/hglobalstream.c

@@ -151,7 +151,10 @@ static HRESULT WINAPI stream_Read(IStream *iface, void *pv, ULONG cb, ULONG *rea
     if (!read_len)
         read_len = &dummy;
 
-    len = min(stream->handle->size - stream->position.u.LowPart, cb);
+    if (stream->handle->size >= stream->position.u.LowPart)
+        len = min(stream->handle->size - stream->position.u.LowPart, cb);
+    else
+        len = 0;
 
     buffer = GlobalLock(stream->handle->hglobal);
     if (!buffer)

dlls/ole32/tests/hglobalstream.c

@@ -65,6 +65,25 @@ static void test_streamonhglobal(void)
     hr = IStream_Write(pStream, data, sizeof(data), NULL);
     ok_ole_success(hr, "IStream_Write");
 
+    /* Seek beyond the end of the stream and read from it */
+    ll.QuadPart = sizeof(data) + 16;
+    hr = IStream_Seek(pStream, ll, STREAM_SEEK_SET, NULL);
+    ok_ole_success(hr, "IStream_Seek");
+
+    hr = IStream_Read(pStream, buffer, sizeof(buffer), &read);
+    ok_ole_success(hr, "IStream_Read");
+    ok(read == 0, "IStream_Read returned read %ld\n", read);
+
+    ull.u.HighPart = 0xCAFECAFE;
+    ull.u.LowPart = 0xCAFECAFE;
+    ll.u.HighPart = 0;
+    ll.u.LowPart = 0;
+    hr = IStream_Seek(pStream, ll, STREAM_SEEK_CUR, &ull);
+    ok_ole_success(hr, "IStream_Seek");
+    ok(ull.u.LowPart == sizeof(data) + 16, "LowPart set to %ld\n", ull.u.LowPart);
+    ok(ull.u.HighPart == 0, "should have set HighPart to 0 instead of %ld\n", ull.u.HighPart);
+
+    /* Seek to the start of the stream and read from it */
     ll.QuadPart = 0;
     hr = IStream_Seek(pStream, ll, STREAM_SEEK_SET, NULL);
     ok_ole_success(hr, "IStream_Seek");