Revert of SegmentedString::push() should always push a char in front

Source/platform/text/SegmentedString.h

Index: Source/platform/text/SegmentedString.h
diff --git a/Source/platform/text/SegmentedString.h b/Source/platform/text/SegmentedString.h
index 7daa101f2a3f980cd9daee06b778a56e77549102..88ffb605caae433f8f3e524b58b758c778e92196 100644
--- a/Source/platform/text/SegmentedString.h
+++ b/Source/platform/text/SegmentedString.h
@@ -190,15 +190,13 @@
 
     void push(UChar c)
     {
-        ASSERT(c);
-
         if (!m_pushedChar1) {
-            m_currentChar = m_pushedChar1 = c;
+            m_pushedChar1 = c;
+            m_currentChar = m_pushedChar1 ? m_pushedChar1 : m_currentString.getCurrentChar();
             updateSlowCaseFunctionPointers();
         } else {
             ASSERT(!m_pushedChar2);
-            m_pushedChar2 = m_pushedChar1;
-            m_currentChar = m_pushedChar1 = c;
+            m_pushedChar2 = c;
         }
     }