fix int -> bool warning

BUG=

Review URL: https://codereview.chromium.org/15737012

git-svn-id: http://skia.googlecode.com/svn/trunk@9243 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index dff79ee..05da5cb 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -52,6 +52,10 @@
     return (T*)luaL_checkudata(L, index, get_mtname(*obj));
 }
 
+static bool lua2bool(lua_State* L, int index) {
+    return !!lua_toboolean(L, index);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static void setfield_string(lua_State* L, const char key[], const char value[]) {
@@ -244,7 +248,7 @@
 }
 
 static int lpaint_setAntiAlias(lua_State* L) {
-    get_obj<SkPaint>(L, 1)->setAntiAlias(lua_toboolean(L, 2));
+    get_obj<SkPaint>(L, 1)->setAntiAlias(lua2bool(L, 2));
     return 0;
 }