Fix "unexpected error type" exception in constructor conversion

So #KT-20218 Fixed

idea/testData/intentions/convertPrimaryConstructorToSecondary/errorType.kt

@@ -0,0 +1,6 @@
+// SKIP_ERRORS_BEFORE
+// SKIP_ERRORS_AFTER
+
+class Foo(val <caret>arg: Int) {
+    val arg = arg
+}

idea/testData/intentions/convertPrimaryConstructorToSecondary/errorType.kt.after

@@ -0,0 +1,13 @@
+// SKIP_ERRORS_BEFORE
+// SKIP_ERRORS_AFTER
+
+class Foo {
+    val arg: Int
+
+    constructor(arg: Int) {
+        this.arg = arg
+        this.arg = arg
+    }
+
+    val arg
+}