font: fix some JS memory leaks

example/app.ts

@@ -55,6 +55,7 @@ fetch(url.href).then(response =>
   for (let i = 33; i <= 126; i++) {
     face_render_glyph(face, atlas, i);
   }
+  //face_render_glyph(face, atlas, "橋".codePointAt(0));
   //face_render_glyph(face, atlas, "p".codePointAt(0));
 
   // Debug our canvas

src/font/Atlas.zig

@@ -392,7 +392,7 @@ pub const Wasm = struct {
         // This will return the same context on subsequent calls so it
         // is important to reset it.
         const ctx = try canvas.call(js.Object, "getContext", .{js.string("2d")});
-        errdefer ctx.deinit();
+        defer ctx.deinit();
 
         // We need to draw pixels so this is format dependent.
         var buf: []u8 = switch (self.format) {

src/font/face/web_canvas.zig

@@ -163,7 +163,6 @@ pub const Face = struct {
         });
 
         // Draw glyph
-        // TODO: may need a +1 on the left/asc here to avoid clipping
         try ctx.set("fillStyle", js.string("black"));
         try ctx.call(void, "fillText", .{
             glyph_str,