C++: Fix resolving of partial specialization

Use-case:
struct b {};
template<class X, class Y> struct s { float f; };
template<class X> struct s<X, b> { int i; };

void f()
{
    s<int, b> var;
    var.i; // i not highlighted
}

Task-number: QTCREATORBUG-14036
Change-Id: I70a87499e0a375e84d992ca0a79d77270a3419e8
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/libs/cplusplus/LookupContext.cpp

@@ -1212,6 +1212,9 @@ LookupScopePrivate *LookupScopePrivate::findSpecialization(
                         }
                     }
                 }
+
+                if (specializationTemplateArgument == initializationTemplateArgument)
+                    return cit->second;
             }
         }
     }