Add missing string cast for non-cv var fetches

Author: nikic

Zend/tests/variable_with_boolean_name.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Variable with boolean name
+--FILE--
+<?php
+
+${true} = 42;
+var_dump(${true});
+var_dump(${'1'});
+
+?>
+--EXPECT--
+int(42)
+int(42)

Zend/zend_compile.c

@@ -1978,6 +1978,9 @@ static zend_op *zend_compile_simple_var_no_cv(znode *result, zend_ast *ast, uint
 	}
 
 	zend_compile_expr(&name_node, name_ast);
+	if (name_node.op_type == IS_CONST) {
+		convert_to_string(&name_node.u.constant);
+	}
 
 	opline = zend_emit_op(result, ZEND_FETCH_R, &name_node, NULL);