Avoid testing isClassDeclaration if there's no valueDeclaration

I'm not sure if this is enough -- perhaps it's better to make the test
dig through the interface/s to the class?

Fixes 36059.

Author: elibarzilay

src/compiler/checker.ts

@@ -16130,6 +16130,7 @@ namespace ts {
                     unmatchedProperty.valueDeclaration
                     && isNamedDeclaration(unmatchedProperty.valueDeclaration)
                     && isPrivateIdentifier(unmatchedProperty.valueDeclaration.name)
+                    && source.symbol.valueDeclaration
                     && isClassDeclaration(source.symbol.valueDeclaration)
                 ) {
                     const privateIdentifierDescription = unmatchedProperty.valueDeclaration.name.escapedText;

tests/baselines/reference/privateNamesUnique-4.errors.txt

@@ -0,0 +1,14 @@
+tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts(6,7): error TS2741: Property '#something' is missing in type 'A2' but required in type 'C'.
+
+
+==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts (1 errors) ====
+    class A1 { }
+    interface A2 extends A1 { }
+    declare const a: A2;
+    
+    class C { #something: number }
+    const c: C = a;
+          ~
+!!! error TS2741: Property '#something' is missing in type 'A2' but required in type 'C'.
+!!! related TS2728 tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts:5:11: '#something' is declared here.
+    

tests/baselines/reference/privateNamesUnique-4.js

@@ -0,0 +1,20 @@
+//// [privateNamesUnique-4.ts]
+class A1 { }
+interface A2 extends A1 { }
+declare const a: A2;
+
+class C { #something: number }
+const c: C = a;
+
+
+//// [privateNamesUnique-4.js]
+var _something;
+class A1 {
+}
+class C {
+    constructor() {
+        _something.set(this, void 0);
+    }
+}
+_something = new WeakMap();
+const c = a;

tests/baselines/reference/privateNamesUnique-4.symbols

@@ -0,0 +1,21 @@
+=== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts ===
+class A1 { }
+>A1 : Symbol(A1, Decl(privateNamesUnique-4.ts, 0, 0))
+
+interface A2 extends A1 { }
+>A2 : Symbol(A2, Decl(privateNamesUnique-4.ts, 0, 12))
+>A1 : Symbol(A1, Decl(privateNamesUnique-4.ts, 0, 0))
+
+declare const a: A2;
+>a : Symbol(a, Decl(privateNamesUnique-4.ts, 2, 13))
+>A2 : Symbol(A2, Decl(privateNamesUnique-4.ts, 0, 12))
+
+class C { #something: number }
+>C : Symbol(C, Decl(privateNamesUnique-4.ts, 2, 20))
+>#something : Symbol(C.#something, Decl(privateNamesUnique-4.ts, 4, 9))
+
+const c: C = a;
+>c : Symbol(c, Decl(privateNamesUnique-4.ts, 5, 5))
+>C : Symbol(C, Decl(privateNamesUnique-4.ts, 2, 20))
+>a : Symbol(a, Decl(privateNamesUnique-4.ts, 2, 13))
+

tests/baselines/reference/privateNamesUnique-4.types

@@ -0,0 +1,16 @@
+=== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts ===
+class A1 { }
+>A1 : A1
+
+interface A2 extends A1 { }
+declare const a: A2;
+>a : A2
+
+class C { #something: number }
+>C : C
+>#something : number
+
+const c: C = a;
+>c : C
+>a : A2
+

tests/cases/conformance/classes/members/privateNames/privateNamesUnique-4.ts

@@ -0,0 +1,8 @@
+// @target: es2015
+
+class A1 { }
+interface A2 extends A1 { }
+declare const a: A2;
+
+class C { #something: number }
+const c: C = a;