Fix a bug for continuations-from-closures that need a local $this

If a continuation in a closure needed a $this variable,
hhir would fail to initialize it, resulting in reads reporting
null.

This didn't come up much, because usually we dont need a variable;
we can typically use This or BareThis. Its only cases where $this
might be passed by reference, or there are dynamic variables that
actually require a local $this.

hphp/runtime/vm/jit/hhbctranslator.cpp

@@ -1026,7 +1026,7 @@ void HhbcTranslator::emitCreateCont(bool getArgs,
       mapContParams(params, origFunc, genFunc)) {
     static auto const thisStr = StringData::GetStaticString("this");
     Id thisId = kInvalidId;
-    const bool fillThis = origFunc->isNonClosureMethod() &&
+    const bool fillThis = origFunc->isMethod() &&
       !origFunc->isStatic() &&
       ((thisId = genFunc->lookupVarId(thisStr)) != kInvalidId) &&
       (origFunc->lookupVarId(thisStr) == kInvalidId);

hphp/test/slow/yield/closure_gen_with_this_loc.php

@@ -0,0 +1,21 @@
+<?php
+
+class X {
+  function gen($fn) {
+    return function() use ($fn) {
+      yield $fn($this);
+    };
+  }
+}
+
+function test() {
+  $x = new X;
+  $f = $x->gen(function($x) { var_dump(get_class($x)); });
+  foreach ($f() as $e) {
+    var_dump($e);
+  }
+}
+
+test();
+
+function fiz($x) { return false; }

hphp/test/slow/yield/closure_gen_with_this_loc.php.expect

@@ -0,0 +1,2 @@
+string(1) "X"
+NULL