Fix build on 32-bit.

Index: src/widgets/GraphGridLayout.cpp
--- src/widgets/GraphGridLayout.cpp.orig
+++ src/widgets/GraphGridLayout.cpp
@@ -547,7 +547,7 @@ void GraphGridLayout::calculateEdgeMainColumn(GraphGri
 
     struct Event
     {
-        size_t blockId;
+        ut64 blockId;
         size_t edgeId;
         int row;
         enum Type { Edge = 0, Block = 1 } type;
