[iOS] Narrow non-breaking space does not fall back to a correct font

[iOS] Narrow non-breaking space does not fall back to a correct font
https://bugs.webkit.org/show_bug.cgi?id=139335

Reviewed by Enrica Casucci.

Source/WebCore:

Test: fast/text/narrow-non-breaking-space.html

* platform/graphics/ios/FontCacheIOS.mm:
(WebCore::requiresCustomFallbackFont):
(WebCore::FontCache::getCustomFallbackFont):

LayoutTests:

* fast/text/narrow-non-breaking-space-expected.html: Added.
* fast/text/narrow-non-breaking-space.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@176971 268f45cc-cd09-0410-ab3c-d52691b4dbfc