Show documentation for a class if the constructor has no docs

#KT-17926 Fixed

idea/testData/editor/quickDoc/OnEmptySecondaryConstructor.kt

@@ -0,0 +1,17 @@
+/**
+Documentation is here.
+ */
+class Foo {
+    private var x: Int = 0
+
+    constructor(x: Int) {
+        this.x = x
+    } //secondary constructor without documentation
+}
+
+fun test() {
+    val f = Foo<caret>(10)
+}
+//INFO: <div class='definition'><pre><a href="psi_element://Foo"><code>Foo</code></a><br>public constructor <b>Foo</b>(
+//INFO:     x: Int
+//INFO: )</pre></div><div class='content'><p>Documentation is here.</p></div><table class='sections'></table>