Fix Too many shorthand attributes error when using a modifier as a function with more than 3 parameters in an expression

Fixes #949

src/Compile/Modifier/IsArrayModifierCompiler.php

@@ -0,0 +1,19 @@
+<?php
+namespace Smarty\Compile\Modifier;
+use Smarty\CompilerException;
+
+/**
+ * Smarty is_array modifier plugin
+ */
+class IsArrayModifierCompiler extends Base {
+
+	public function compile($params, \Smarty\Compiler\Template $compiler) {
+
+		if (count($params) !== 1) {
+			throw new CompilerException("Invalid number of arguments for is_array. is_array expects exactly 1 parameter.");
+		}
+
+		return 'is_array(' . $params[0] . ')';
+	}
+
+}