<https://bugs.webkit.org/show_bug.cgi?id=62666>

<https://bugs.webkit.org/show_bug.cgi?id=62666>
<rdar://problem/9606676>
Callers should be robust against WebImage::create() returning an image with a null snapshot

Reviewed by Dan Bernstein.

* Shared/API/c/cg/WKImageCG.cpp:
(WKImageCreateCGImage):
Return 0 if no bitmap was created.
(WKImageCreateFromCGImage):
Ditto.

* Shared/UserMessageCoders.h:
(WebKit::UserMessageEncoder::baseEncode):
Check for null before dereferencing image->bitmap() in two places.

* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::snapshotInViewCoordinates):
Return 0 if no bitmap was created.
(WebKit::WebPage::scaledSnapshotInDocumentCoordinates):
Ditto.
(WebKit::WebPage::createSnapshotOfVisibleContent):
Bail out if no bitmap was created.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@88856 268f45cc-cd09-0410-ab3c-d52691b4dbfc