[Sema] Fixes templated friend member assertion

[Mordante]

Summary

Fixes https://bugs.llvm.org/show_bug.cgi?id=41792

clang/lib/Sema/SemaTemplate.cpp

struct DependencyChecker : RecursiveASTVisitor<DependencyChecker> {
   }
 };
 } // end anonymous namespace
 
 /// Determines whether a given type depends on the given parameter
 /// list.
 static bool
 DependsOnTemplateParameters(QualType T, TemplateParameterList *Params) {
+  if (!Params->size())
+    return false;
+
   DependencyChecker Checker(Params, /*IgnoreNonTypeDependent*/false);
   Checker.TraverseType(T);
   return Checker.Match;
 }
 
 // Find the source range corresponding to the named type in the given
 // nested-name-specifier, if any.
 static SourceRange getRangeOfTypeInNestedNameSpecifier(ASTContext &Context,

clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp

 // RUN: %clang_cc1 -fsyntax-only -verify %s
 template<typename T>
 void f(T);
 
 template<typename T>
-struct A { };
+struct A { }; // expected-note{{template is declared here}}
 
 struct X {
   template<> friend void f<int>(int); // expected-error{{in a friend}}
   template<> friend class A<int>; // expected-error{{cannot be a friend}}
   
   friend void f<float>(float); // okay
   friend class A<float>; // okay
 };
+
+struct PR41792 {
+  // expected-error@+1{{cannot declare an explicit specialization in a friend}}
+  template <> friend void f<>(int);
+
+  // expected-error@+2{{template specialization declaration cannot be a friend}}
+  // expected-error@+1{{too few template arguments for class template 'A'}}
+  template <> friend class A<>;
+};