Fix SemaTemplate/instantiate-field.cpp after r261297.

For templates, fields can have incomplete types:

  template <class T>
  struct A2 {
    struct B;
    B b;
  };

Don't try to touch the DefinitionData of those fields.

llvm-svn: 261301
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index c8edd5a..e84b913 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -704,7 +704,7 @@
 
     if (!Field->hasInClassInitializer() && !Field->isMutable()) {
       if (CXXRecordDecl *FieldType = Field->getType()->getAsCXXRecordDecl()) {
-        if (!FieldType->allowConstDefaultInit())
+        if (FieldType->hasDefinition() && !FieldType->allowConstDefaultInit())
           data().HasUninitializedFields = true;
       } else {
         data().HasUninitializedFields = true;