Bug 1719545 - Part 4: Fallback to script extension even it only has one extension or its own script code. r=jfkthame

Differential Revision: https://phabricator.services.mozilla.com/D131514

gfx/thebes/gfxScriptItemizer.cpp

@@ -206,8 +206,11 @@ bool gfxScriptItemizer::Next(uint32_t& aRunStart, uint32_t& aRunLimit,
           // store for use in the event the run remains unresolved.
           mozilla::intl::ScriptExtensionVector extensions;
           auto extResult = mozilla::intl::Script::GetExtensions(ch, extensions);
-          if (extResult.isOk() && extensions.length() > 1) {
-            fallbackScript = Script(extensions[0]);
+          if (extResult.isOk()) {
+            Script ext = Script(extensions[0]);
+            if (!CanMergeWithContext(ext)) {
+              fallbackScript = ext;
+            }
           }
         }
       }