Placeholder didn't hide if `src` was not encoded

[vedtam]

Images URIs fed into iron-image not being properly encoded fail this check:

if (this.$.img.src !== this._resolveSrc(this.src)) {
          return;
 }

because this.$.img.src gets automatically encoded but this.src not. encodeURI(testSrc) fixed the issue for me.

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[vedtam]

I signed it!

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