Compare both first and last names when sorting (#1487)

If two names have the same last name, ensure we fall back on the
first name when sorting them.

// FREEBIE

Podfile.lock

@@ -132,7 +132,7 @@ EXTERNAL SOURCES:
 
 CHECKOUT OPTIONS:
   SignalServiceKit:
-    :commit: 3083e2929c7dcfe5c60e003dd77c310d26dab177
+    :commit: 34ffce89f59356ab23f290866b1c3437f03312ce
     :git: https://github.com/WhisperSystems/SignalServiceKit.git
   SocketRocket:
     :commit: 41b57bb2fc292a814f758441a05243eb38457027

Signal/src/contact/OWSContactsManager.m

@@ -385,46 +385,10 @@ void onAddressBookChanged(ABAddressBookRef notifyAddressBook, CFDictionaryRef in
             signalContacts[contact.textSecureIdentifiers.firstObject] = contact;
         }
     }
-    return [signalContacts.allValues sortedArrayUsingComparator:[[self class] contactComparator]];
-}
-
-+ (NSComparator)contactComparator {
-    return ^NSComparisonResult(id obj1, id obj2) {
-      Contact *contact1 = (Contact *)obj1;
-      Contact *contact2 = (Contact *)obj2;
 
     BOOL firstNameOrdering = ABPersonGetSortOrdering() == kABPersonCompositeNameFormatFirstNameFirst ? YES : NO;
-
-      if (firstNameOrdering) {
-          if (contact1.firstName) {
-              if (contact2.firstName) {
-                  return [contact1.firstName caseInsensitiveCompare:contact2.firstName];
-              } else {
-                  return [contact1.firstName caseInsensitiveCompare:contact2.lastName];
-              }
-          } else {
-              if (contact2.firstName) {
-                  return [contact1.lastName caseInsensitiveCompare:contact2.firstName];
-              } else {
-                  return [contact1.lastName caseInsensitiveCompare:contact2.lastName];
-              }
-          }
-      } else {
-          if (contact1.lastName) {
-              if (contact2.lastName) {
-                  return [contact1.lastName caseInsensitiveCompare:contact2.lastName];
-              } else {
-                  return [contact1.lastName caseInsensitiveCompare:contact2.firstName];
-              }
-          } else {
-              if (contact2.lastName) {
-                  return [contact1.firstName caseInsensitiveCompare:contact2.lastName];
-              } else {
-                  return [contact1.firstName caseInsensitiveCompare:contact2.firstName];
-              }
-          }
-      };
-    };
+    NSComparator contactsComparator = [Contact comparatorSortingNamesByFirstThenLast:firstNameOrdering];
+    return [signalContacts.allValues sortedArrayUsingComparator:contactsComparator];
 }
 
 - (NSArray<Contact *> *)signalContacts {