Don't call PutString with an empty string. Both DumpChildrenAscii and EndAscii can return without modifyting the string, so we need to check the string before calling PutString. This used to cause a crash.

code/FBXExportNode.cpp

@@ -252,6 +252,7 @@ void FBX::Node::DumpChildren(
     } else {
         std::ostringstream ss;
         DumpChildrenAscii(ss, indent);
+        if (ss.tellp() > 0)
             s.PutString(ss.str());
     }
 }
@@ -266,6 +267,7 @@ void FBX::Node::End(
     } else {
         std::ostringstream ss;
         EndAscii(ss, indent, has_children);
+        if (ss.tellp() > 0)
             s.PutString(ss.str());
     }
 }