Handle proper substraction of unsigned numbers.

diff --git a/dlls/opengl32/wgl.c b/dlls/opengl32/wgl.c
index 4d5a257..05d7ce1 100644
--- a/dlls/opengl32/wgl.c
+++ b/dlls/opengl32/wgl.c
@@ -595,7 +595,7 @@
 	glNewList(listBase++, GL_COMPILE);
 	if (needed_size != 0) {
 	    glBitmap(gm.gmBlackBoxX, gm.gmBlackBoxY,
-		     0 - gm.gmptGlyphOrigin.x, gm.gmBlackBoxY - gm.gmptGlyphOrigin.y,
+		     0 - (int) gm.gmptGlyphOrigin.x, (int) gm.gmBlackBoxY - (int) gm.gmptGlyphOrigin.y,
 		     gm.gmCellIncX, gm.gmCellIncY,
 		     gl_bitmap);
 	} else {