Crash when laying out (char)0

https://bugs.webkit.org/show_bug.cgi?id=143103

Reviewed by Dean Jackson.

We currently cache a character -> Font mapping in a HashMap.
However, keys in Hashmaps can't be 0. This patch simply skips
the cache in this case.

No new tests, for now. I'm having trouble creating a test because
the site that causes this bug generates their page using script,
and the script is all minified, and difficult to understand. I
will contact the owner of the site and ask for and unminified
version of their sources. However, I don't want to that to block
this tiny fix from going in.

* platform/graphics/Font.cpp:
(WebCore::Font::systemFallbackFontForCharacter):

Canonical link: https://commits.webkit.org/161124@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@182015 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,24 @@
+2015-03-26  Myles C. Maxfield  <mmaxfield@apple.com>
+
+        Crash when laying out (char)0
+        https://bugs.webkit.org/show_bug.cgi?id=143103
+
+        Reviewed by Dean Jackson.
+
+        We currently cache a character -> Font mapping in a HashMap.
+        However, keys in Hashmaps can't be 0. This patch simply skips
+        the cache in this case.
+
+        No new tests, for now. I'm having trouble creating a test because
+        the site that causes this bug generates their page using script,
+        and the script is all minified, and difficult to understand. I
+        will contact the owner of the site and ask for and unminified
+        version of their sources. However, I don't want to that to block
+        this tiny fix from going in.
+
+        * platform/graphics/Font.cpp:
+        (WebCore::Font::systemFallbackFontForCharacter):
+
 2015-03-26  Jer Noble  <jer.noble@apple.com>
 
         [Mac][EME] Crash at com.apple.WebCore: WebCore::CDMSessionMediaSourceAVFObjC::releaseKeys + 177

Source/WebCore/platform/graphics/Font.cpp

@@ -415,6 +415,11 @@ RefPtr<Font> Font::systemFallbackFontForCharacter(UChar32 character, const FontD
 {
     auto fontAddResult = systemFallbackCache().add(this, CharacterFallbackMap());
 
+    if (!character) {
+        UChar codeUnit = 0;
+        return FontCache::singleton().systemFallbackForCharacters(description, this, isForPlatformFont, &codeUnit, 1);
+    }
+
     auto key = std::make_pair(character, isForPlatformFont);
     auto characterAddResult = fontAddResult.iterator->value.add(key, nullptr);