Fix headway during optimizeReloc()

Later: "Assertion `(soxrelocs == 0) == !has_oxrelocs' failed."
https://github.com/upx/upx/issues/552
	modified:   packer.cpp
	modified:   packer.h
	modified:   pefile.cpp

src/packer.h

@@ -311,6 +311,7 @@ protected:
     // compression buffers
     MemBuffer ibuf; // input
     MemBuffer obuf; // output
+    unsigned ibufgood;  // high-water mark in ibuf (pefile.cpp)
 
     // UI handler
     UiPacker *uip = nullptr;