fix segfault

Don't assume we are in a function.

hphp/compiler/parser/parser.cpp

@@ -400,7 +400,9 @@ void Parser::onCall(Token &out, bool dynamic, Token &name, Token &params,
   } else {
     const string &s = name.text();
     if (s == "func_num_args" || s == "func_get_args" || s == "func_get_arg") {
-      m_hasCallToGetArgs.back() = true;
+      if (m_hasCallToGetArgs.size() > 0) {
+        m_hasCallToGetArgs.back() = true;
+      }
     }
 
     SimpleFunctionCallPtr call

hphp/test/zend/good/zend/020.php

@@ -0,0 +1,18 @@
+<?php
+
+var_dump(func_get_arg(1,2,3));
+var_dump(func_get_arg(1));
+var_dump(func_get_arg());
+
+function bar() {
+	var_dump(func_get_arg(1));
+}
+
+function foo() {
+	bar(func_get_arg(1));
+}
+
+foo(1,2);
+
+echo "Done\n";
+?>

hphp/test/zend/good/zend/020.php.expectf

@@ -0,0 +1,9 @@
+HipHop Warning: %a
+NULL
+HipHop Warning: %a
+bool(false)
+HipHop Warning: %a
+NULL
+HipHop Warning: %a
+bool(false)
+Done

hphp/tools/import_zend_test.py

@@ -35,7 +35,6 @@ no_import = (
     '/tests/run-test/test010.phpt',
 
     # segfaults
-    '/Zend/tests/020.phpt',
     '/Zend/tests/bug35239.phpt',
     '/Zend/tests/bug54265.phpt',
     '/Zend/tests/bug55705.phpt',