fix couple of bugs in constructor signature serialization/parsing

compiler/testData/writeSignature/constructor/Constructor0.kt

@@ -0,0 +1,6 @@
+class Constructor0()
+
+// method: Constructor0::<init>
+// jvm signature:     ()V
+// generic signature: null
+// kotlin signature:  null

compiler/testData/writeSignature/constructor/ConstructorWithTypeParameter.kt

@@ -0,0 +1,6 @@
+class ConstructorWithTypeParameter<P>()
+
+// method: ConstructorWithTypeParameter::<init>
+// jvm signature:     (Ljet/TypeInfo;)V
+// generic signature: null
+// kotlin signature:  null

compiler/testData/writeSignature/constructor/ConstructorWithTypeParameterAndValueParameterP.kt

@@ -0,0 +1,6 @@
+class ConstructorWithTypeParameter<P>(p: P)
+
+// method: ConstructorWithTypeParameter::<init>
+// jvm signature:     (Ljet/TypeInfo;Ljava/lang/Object;)V
+// generic signature: (Ljet/TypeInfo;TP;)V
+// kotlin signature:  null