优化新设备判断逻辑。Review by 硬币。

@@ -408,9 +408,8 @@ static NSString * const kYohoBuyUsedDevice = @"com.yoho.buy.useddevice";
 
 + (BOOL) isNewDevice
 {
-    static NSString * usedDevice = nil;
-    
-    if ([usedDevice isEqualToString:@"Y"]) {
+    static BOOL isNew = YES;
+    if (isNew == NO) {
         return NO;
     }
     
@@ -418,7 +417,7 @@ static NSString * const kYohoBuyUsedDevice = @"com.yoho.buy.useddevice";
     if (yohoinfoKVPairs == nil || yohoinfoKVPairs[kYohoBuyUsedDevice] == nil) {
         return YES;
     } else {
-        usedDevice = [NSString stringWithString:yohoinfoKVPairs[kYohoBuyUsedDevice]];
+        isNew = NO;
         return NO;
     }
 }