Fix caching of small inline images in Parser.makeInlineImage (issue 8790)
*Follow-up to PR 5445.*
Using the PDF file from issue 2618, i.e. http://bugzilla-attachments.gnome.org/attachment.cgi?id=226471, with the following manifest file:
```json
[
{ "id": "issue2618",
"file": "../web/pdfs/issue2618.pdf",
"md5": "",
"rounds": 50,
"type": "eq"
}
]
```
I get the following results when comparing `master` against this patch:
```
browser | stat | Count | Baseline(ms) | Current(ms) | +/- | % | Result(P<.05)
------- | ------------ | ----- | ------------ | ----------- | ---- | ------ | -------------
firefox | Overall | 50 | 4694 | 3974 | -721 | -15.35 | faster
firefox | Page Request | 50 | 2 | 1 | 0 | -22.83 |
firefox | Rendering | 50 | 4692 | 3972 | -720 | -15.35 | faster
```
So, based on these results, it seems like a fairly clear win to fix this broken caching :-)