[ir] Catch invalid matrix element in decode

If the matrix element type was invalid, do not try to create the
matrix column type.

Fixed: 446116232
Change-Id: Ie72cc58ea9f51e499717c9eab930859d069373cf
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/262555
Reviewed-by: dan sinclair <[email protected]>
Commit-Queue: James Price <[email protected]>

Author: jrprice

src/tint/lang/core/ir/binary/decode.cc

@@ -781,6 +781,10 @@ struct Decoder {
             return mod_out_.Types().invalid();
         }
         auto* el_ty = Type(matrix_in.element_type());
+        if (el_ty == nullptr) {
+            err_ << "matrix element type is invalid\n";
+            return mod_out_.Types().invalid();
+        }
         auto* column_ty = mod_out_.Types().vec(el_ty, matrix_in.num_rows());
         return mod_out_.Types().mat(column_ty, matrix_in.num_columns());
     }