Fix a gcc 4.6 compiler warning.

public/common/unicode/unistr.h

Index: public/common/unicode/unistr.h
diff --git a/public/common/unicode/unistr.h b/public/common/unicode/unistr.h
index 57ea34652d67cfba6eba22b1b584bdbfe07ad197..46b9d95145eeac6e03c9746b8566513ccb5b2627 100644
--- a/public/common/unicode/unistr.h
+++ b/public/common/unicode/unistr.h
@@ -4021,8 +4021,7 @@ UnicodeString::replace(int32_t start,
                UChar32 srcChar) {
   UChar buffer[U16_MAX_LENGTH];
   int32_t count = 0;
-  UBool isError = FALSE;
-  U16_APPEND(buffer, count, U16_MAX_LENGTH, srcChar, isError);
+  U16_APPEND_UNSAFE(buffer, count, srcChar);
   return doReplace(start, _length, buffer, 0, count);
 }
 
@@ -4324,8 +4323,7 @@ inline UnicodeString&
 UnicodeString::append(UChar32 srcChar) {
   UChar buffer[U16_MAX_LENGTH];
   int32_t _length = 0;
-  UBool isError = FALSE;
-  U16_APPEND(buffer, _length, U16_MAX_LENGTH, srcChar, isError);
+  U16_APPEND_UNSAFE(buffer, _length, srcChar);
   return doReplace(length(), 0, buffer, 0, _length);
 }