Change fillRect() to take a buffer instead of a pixel

There has been some confusion if fillRect() should accept a buffer
or a pixel. This can cause misrendering if your data is not in the
native endian order. A buffer makes more sense here though, and
is what most of the callers are already assuming, so change the
API to follow that.
diff --git a/common/rfb/zrleDecode.h b/common/rfb/zrleDecode.h
index 42b28b3..2566171 100644
--- a/common/rfb/zrleDecode.h
+++ b/common/rfb/zrleDecode.h
@@ -73,7 +73,7 @@
 
       if (palSize == 1) {
         PIXEL_T pix = palette[0];
-        pb->fillRect(pf, t, pix);
+        pb->fillRect(pf, t, &pix);
         continue;
       }