KT-1536: parse Throwable as nullable in JavaDescriptorResolver

compiler/testData/readJavaBinaryClass/MyException.java

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+// http://youtrack.jetbrains.com/issue/KT-1536
+
+package test;
+
+class MyException {
+    MyException(String message, Throwable cause) {}
+}

compiler/testData/readJavaBinaryClass/MyException.kt

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+package test
+
+open class MyException(p0: String?, p1: Throwable?)

compiler/testData/readJavaBinaryClass/MyException.txt

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+namespace test
+
+open class test.MyException : jet.Any {
+    final /*constructor*/ fun <init>(/*0*/ p0: jet.String?, /*1*/ p1: jet.Throwable?): test.MyException
+}