round() instead of truncating in two-pass OpenGL area scaling

BitmapTest::testScale2() on Linux fails for me without this,
as the two-pass setup higher truncates the size to integers, and
truncating here again sets the final size as 64 instead of the expected 65

Change-Id: I54748e29f0e0ca63539e42009759a93d6a5d6be2
Reviewed-on: https://gerrit.libreoffice.org/70779
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

vcl/opengl/scale.cxx

@@ -284,8 +284,8 @@ bool OpenGLSalBitmap::ImplScaleArea( const rtl::Reference< OpenGLContext > &xCon
         mnWidth = nNewWidth;
         mnHeight = nNewHeight;
 
-        nNewWidth = int(mnWidth * rScaleX);
-        nNewHeight = int (mnHeight * rScaleY);
+        nNewWidth = round(mnWidth * rScaleX);
+        nNewHeight = round(mnHeight * rScaleY);
 
         ixscale = 1 / rScaleX;
         iyscale = 1 / rScaleY;