fix: guard against falsy options arguments

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---

Author: kgryte

lib/node_modules/@stdlib/stats/tools/reduce/unary-strided-dispatch/lib/main.js

@@ -310,6 +310,7 @@ setReadOnly( UnaryStridedDispatch.prototype, 'assign', function assign( x ) {
 	var arr;
 	var err;
 	var tmp;
+	var flg;
 	var dt;
 	var N;
 	var f;
@@ -341,6 +342,7 @@ setReadOnly( UnaryStridedDispatch.prototype, 'assign', function assign( x ) {
 	// If we processed all but the last argument, assume that the last argument is an options argument...
 	else if ( i === nargs-1 ) {
 		options = arguments[ i ];
+		flg = true;
 	}
 	// Otherwise, if we have more than one argument remaining, then at least one argument is not an ndarray but should be...
 	else if ( i < nargs-1 ) {
@@ -356,7 +358,7 @@ setReadOnly( UnaryStridedDispatch.prototype, 'assign', function assign( x ) {
 	// Validate any provided options...
 	N = ndims( x );
 	opts = objectAssign( {}, defaults );
-	if ( options ) {
+	if ( flg ) {
 		err = validate( opts, N, this._odtypes, options );
 		if ( err ) {
 			throw err;