fixes #3498

Previously it was not possible to use template arguments in template body as
the symbols were not resolved correctly leading to Error: undeclared
identifier: 'XX', eg.:

   template defaultOf[T](t: T): expr = (var d: T; d)
   echo defaultOf(1) #<- invalid identifier, but should output 0

compiler/evaltempl.nim

@@ -38,7 +38,8 @@ proc evalTemplateAux(templ, actual: PNode, c: var TemplCtx, result: PNode) =
     if s.owner.id == c.owner.id:
       if s.kind == skParam and sfGenSym notin s.flags:
         handleParam actual.sons[s.position]
-      elif s.kind == skGenericParam:
+      elif s.kind == skGenericParam or
+           s.kind == skType and s.typ != nil and s.typ.kind == tyGenericParam:
         handleParam actual.sons[s.owner.typ.len + s.position - 1]
       else:
         internalAssert sfGenSym in s.flags