tdf#120703 PVS: do not split a band that is just one pixel high

This is what mentioned in the comment to the line, so implement just that

V560 A part of conditional expression is always true:
     pBand->mnYTop < pBand->mnYBottom.

Change-Id: I1027a30a07d49940a31838deddb457b6379eb887
Reviewed-on: https://gerrit.libreoffice.org/64399
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

vcl/source/gdi/region.cxx

@@ -146,7 +146,7 @@ namespace
                        // this allows the lowest pixel of the band to be split off
                     && pBand->mnYBottom>=nTop
                        // do not split a band that is just one pixel high
-                    && pBand->mnYTop<pBand->mnYBottom)
+                    && pBand->mnYTop<pBand->mnYBottom-1)
                 {
                     // Split the top band.
                     pTopBand = pBand->SplitBand(nTop);
@@ -163,7 +163,7 @@ namespace
                        // prevent splitting off a band that is 0 pixel high
                     && pBand->mnYBottom>nBottom
                        // do not split a band that is just one pixel high
-                    && pBand->mnYTop<pBand->mnYBottom)
+                    && pBand->mnYTop<pBand->mnYBottom-1)
                 {
                     // Split the bottom band.
                     pBand->SplitBand(nBottom+1);