KT-4152 Wrong postfix increment/decrement calculation

#KT-4152 Fixed

compiler/testData/codegen/box/operatorConventions/kt4152.kt

@@ -0,0 +1,29 @@
+public var inc: Int = 0;
+
+public var propInc: Int = 0
+    get() {inc++; return $propInc}
+    set(a: Int) {
+        inc++
+        $propInc = a
+    }
+
+public var dec: Int = 0;
+
+public var propDec: Int = 0;
+    get() { dec--; return $propDec}
+    set(a: Int) {
+        dec--
+        $propDec = a
+    }
+
+fun box(): String {
+    propInc++
+    if (inc != 2) return "fail in postfix increment: ${inc} != 2"
+    if (propInc != 1) return "fail in postfix increment: ${propInc} != 1"
+
+    propDec--
+    if (dec != -2) return "fail in postfix decrement: ${dec} != -2"
+    if (propDec != -1) return "fail in postfix decrement: ${propDec} != -1"
+
+    return "OK"
+}