when calling function stored in local variable as unary operation, don't forget to push function instance (KT-1953)

I'm sure that there are similar cases that still don't work;  please let me know if you find any
#KT-1953 fixed

compiler/testData/codegen/regressions/kt1953.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    val sb = StringBuilder()
+    fun String.plus() {
+        sb.append(this)
+    }
+
+    +"OK"
+    return sb.toString()!!
+}

compiler/testData/codegen/regressions/kt1953_class.kt

@@ -0,0 +1,14 @@
+class A {
+    private val sb: StringBuilder = StringBuilder()
+
+    fun String.plus {
+        sb.append(this)
+    }
+
+    fun foo(): String {
+        +"OK"
+        return sb.toString()!!
+    }
+}
+
+fun box(): String = A().foo()