Fix potential uninitialized variable in clipper (#5881)

* Fix potential uninitialized variable in clipper

* Clipper: Fix second parameter as well.

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Co-authored-by: Kim Kulling <[email protected]>

contrib/clipper/clipper.cpp

@@ -1567,7 +1567,7 @@ bool Clipper::ExecuteInternal()
     m_SortedEdges = 0;
 
     succeeded = true;
-    cInt botY, topY;
+    cInt botY = 0, topY = 0;
     if (!PopScanbeam(botY)) return false;
     InsertLocalMinimaIntoAEL(botY);
     while (PopScanbeam(topY) || LocalMinimaPending())