JitBackpatch: fix NOP padding

The new NOP emitter breaks when called with a negative count. As it
turns out, it did happen when deoptimizing 8 bit MOVs because they are
only 4 bytes long and need no BSWAP.

Source/Core/Common/x64Emitter.h

@@ -290,7 +290,7 @@ public:
 	void INT3();
 
 	// Do nothing
-	void NOP(int count = 1);
+	void NOP(size_t count = 1);
 
 	// Save energy in wait-loops on P4 only. Probably not too useful.
 	void PAUSE();