Fix PDL verifiers to be resilient to invalid IR

This would cause a crash when calling `dump()` on an operation that
didn't have a parent yet.

mlir/lib/Dialect/PDL/IR/PDL.cpp

@@ -48,7 +48,7 @@ static bool hasBindingUse(Operation *op) {
 /// is used by a "binding" operation. On failure, emits an error.
 static LogicalResult verifyHasBindingUse(Operation *op) {
   // If the parent is not a pattern, there is nothing to do.
-  if (!isa<PatternOp>(op->getParentOp()))
+  if (!llvm::isa_and_nonnull<PatternOp>(op->getParentOp()))
     return success();
   if (hasBindingUse(op))
     return success();
@@ -265,7 +265,7 @@ static LogicalResult verifyResultTypesAreInferrable(OperationOp op,
 }
 
 LogicalResult OperationOp::verify() {
-  bool isWithinRewrite = isa<RewriteOp>((*this)->getParentOp());
+  bool isWithinRewrite = isa_and_nonnull<RewriteOp>((*this)->getParentOp());
   if (isWithinRewrite && !getOpName())
     return emitOpError("must have an operation name when nested within "
                        "a `pdl.rewrite`");