Steps to Reproduce

the following case reproduces the error:

	<div width="200px" height="200px" style="border: 1px solid red">
		<hlayout vflex="1" hflex="1" style="border: 3px solid blue">
			<gmaps vflex="1" hflex="1" />
		</hlayout>
	</div>

Current Result

JS error:

zk.wpd:350 Uncaught TypeError: Cannot read property 'firstChild' of undefined
    at b.sync (zk.wpd:350)
    at b._tryBind (gmaps.wpd:3)
    at gmaps.wpd:3
    at Object.b.callback (gmaps.wpd:2)
    at a (gmaps.wpd:2)
    at gmaps.wpd:2

Expected Result

no error

Debug Info

The problem doesn't happen with vlayout or div around the gmaps.
However the error can be reproduced also by applying an "inline-block" style to a div.

	<div width="200px" height="200px" >
		<div vflex="1" hflex="1" style="border: 3px solid blue">
			<div vflex="1" hflex="1" style="display: inline-block;">
				<gmaps vflex="1" hflex="1" />
			</div>
		</div>
	</div>

Root Cause

the mask is rendered at a moment where then surrounding div is not yet sized, so it is potentially invisible, or the mask is rendered at an incorrect size not showing the loading message at all.

It should be considered to initialize the loading mask only after the size calculations are finished.

Workaround

adding a "min-width: 1px" to the gmaps component prevents this issue

<gmaps vflex="1" hflex="1" style="min-width: 1px"/>