Jit64: really fix fmrx regression

This is more tricky than I thought!

Source/Core/Core/Src/PowerPC/Jit64/Jit_FloatingPoint.cpp

@@ -224,15 +224,26 @@ void Jit64::fmrx(UGeckoInstruction inst)
 {
 	INSTRUCTION_START
 	JITDISABLE(bJITFloatingPointOff)
-	if (inst.Rc) {
+	if (inst.Rc)
+	{
 		Default(inst); return;
 	}
 	int d = inst.FD;
 	int b = inst.FB;
-	if (d != b) {
+	if (d != b)
+	{
 		fpr.Lock(b, d);
-		fpr.BindToRegister(d);
-		MOVSD(fpr.RX(d), fpr.R(b));
+
+		// we don't need to load d, but if it already is, it must be marked as dirty
+		if (fpr.IsBound(d))
+		{
+			fpr.BindToRegister(d);
+		}
+		fpr.BindToRegister(b, true, false);
+
+		// caveat: the order of ModRM:r/m, ModRM:reg is deliberate!
+		// "MOVSD reg, mem" zeros out the upper half of the destination register
+		MOVSD(fpr.R(d), fpr.RX(b));
 		fpr.UnlockAll();
 	}
 }