Clip bottom coordinates.

dlls/ddraw/dsurface/dib.c

diff --git a/dlls/ddraw/dsurface/dib.c b/dlls/ddraw/dsurface/dib.c
index 2e71506..e2a4f62 100644
--- a/dlls/ddraw/dsurface/dib.c
+++ b/dlls/ddraw/dsurface/dib.c
@@ -395,6 +395,11 @@
 	}
     }
 
+    if (xsrc.bottom > sdesc.dwHeight)
+	xsrc.bottom = sdesc.dwHeight;
+    if (xdst.bottom > ddesc.dwHeight)
+	xdst.bottom = ddesc.dwHeight;
+    
     if (src) assert((xsrc.bottom-xsrc.top) <= sdesc.dwHeight);
     assert((xdst.bottom-xdst.top) <= ddesc.dwHeight);