Prevent null dereference read in `SpecializeType()`
Prevent null dereference read in `SpecializeType()`

For some adversarial protos, the attribute for a key might not exist.

PiperOrigin-RevId: 408382090
Change-Id: Ie7eabe532c9ff280fce5dce1f6cdb93c76c2e040

paolodedios/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-tensorflow/tensorflow,paolodedios/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer,paolodedios/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,Intel-Corporation/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,paolodedios/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,yongtang/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow,gautam1858/tensorflow,Intel-Corporation/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-Corporation/tensorflow,gautam1858/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,Intel-tensorflow/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,gautam1858/tensorflow,yongtang/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,yongtang/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,karllessard/tensorflow,karllessard/tensorflow,tensorflow/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,karllessard/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-tensorflow/tensorflow,yongtang/tensorflow,karllessard/tensorflow,yongtang/tensorflow,Intel-Corporation/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,Intel-tensorflow/tensorflow,karllessard/tensorflow,yongtang/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,karllessard/tensorflow,karllessard/tensorflow,Intel-tensorflow/tensorflow,karllessard/tensorflow